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In preparing the other figures on Dolatocrinus I have had the help of Dr. This in connection with the types of the later described species - mainly in the Walker Museum of the University. Technocrinus may be regarded as an intermediate form, the former species, nowhere described, being of the latter type.

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THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES, bulging is due to the great enlargement and asymmetrical swelling

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The main resulting difference to be noted is in the number and depth of incorporation of fixed needles. IlBr, has a needle incorporated into the outer side of the dichotomy, the base of which can also be sutured. IIBrg has one free needle on the inside of the dichotomy and IIBr^ has two free needles, one on each side.

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THE FOSSIL CRINOIP GENUS DOLATOCRINUS AXD ITS ALLIES. 9 With the incorporation of the lower pinnules in the calyx wall by

The most remarkable thing about this form, however, is the condition of the base. Although their presence is indicated by crenulae in small notches at the junction of the radials, the basals have been virtually eliminated from the calyx. In the three specimens showing these parts they are entirely absent, the proximal margin of the radials being deeply incised with. lobes of the axial canal. the massive face of the column encompassed the entire base, including the radials. and part of the following range; and the basals, thus closed from the exterior, are apt to disappear by atrophy.

THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 13 shallow calyx, with a low tegmen composed of innumerable slightly

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The other genus which must be placed further back in the time scale is Stereocrinus, hitherto restricted to the Middle Devonian, but which now appears in the Helderberg as a well-marked species, for which. In the material obtained by my collectors, Pate and Braun, from the Linden Formation at various places in BentonCounty, Tennes-. The tegmen is evenly convex, appears too high in the depicted specimen due to pinching, and is composed of smooth.

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The cogs may be limited to the width of the nodes to which they are attached, or they may extend either .. way in the span of several internodals, perhaps in some cases connecting and forming continuous jagged longitudinal ridges along the column. Specimens with any part of the column attached, or even any considerable length of detached column, are extremely rare, so .. we have little information on the distribution of the nodal col- . umnals throughout the stem as a whole; but from the fragments available, and from analogy with the mode of growth of the stem in the crinoids in general, it is probable that in the proximal parts of the stem the nodes are continuous, and hide the interpolated internodals under the arch formed by their flanges, while towards the distal end the internodals increase in number, and the intervals .. between the nodes become longer. Thus in the part of the stem proximal to the calyx shown in figure 2 on plate 10, node-col-. umnals are in close contact, concealing the internodals, which can be seen at the broken extremity, and the projecting cogs form continuous ridges.

THE SPECIES OF DOLATOCRINUS

The crinoid-bearing exposures in the Hamilton beds of this area are very limited and are mainly confined to a few miles opposite Louisville and along Silver Creek and other streams in Clark County, Indiana, from which the species of nearly all 53 supposed species were derived and varieties. The occurrence of such an incredible number of species of one genus from one horizon in the same locality is in the highest degree improbable; and merely stating the above facts. Several hundred species of crinoids and blastoids have been described and illustrated in the reports of the Geological Surveys of Missouri and Indiana alone by Miller, chiefly from specimens in the rich collection collected by Mr.

THE FOSSIL CEINOID GENUS DOLATOCRINUS AND ITS ALLIES. 21 by this means they were reheved of the trouble of comparison with

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However, the central nodes may be essentially isolated, but even then there is usually some trace of a connection marking the course of the buried nerve cords. These processes will produce extremes of the two types of sculpture, between which there may be an infinite number of combinations in which the two are more or less mixed. If certain lines of the triangles are highlighted, a star figure is created around the base.

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If the arm gets free on the first. secundibrach, there may be no pores through the calyx wall, or only a single one on one or both sides of the arm base; if higher seconds brackets are incorporated, the number increases accordingly. On the contrary, it is a character of great value and of wide application, representing progressive stages in the ontogeny of the crinoids which often become fixed, and providing decisive criteria in the separation of groups. The whole Larviformia section of the Inadunate is characterized by the arms being in the primitive stage, without any axillary plate in the ray, and thus five in.

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THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 27 ONONDAGA SPECIES

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THE FOSSIL CKINOID GENUS DOLATOCRINUS AND ITS ALLIES. 29

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The entire facies of this form bears a strong resemblance to New York. This magnificent Species is most aptly named, not only on account of its great size, but on account of the decisive manner in which it stands out among all the species of the genus, so perfectly distinct that there are. The specimen on which it was described, though excellent in some respects, was not capable of exhibiting all the characters, especially those of the base.

THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 33

THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 35 wise to enable them to give a recognizable definition from which

THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 37 diameter shows no material departure from the typical characters

HAMILTON SPECIES

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Tenarmed species of medium to large size, and strongly ornamented, the former with sharp radiating striae and the latter with interrupted lines or pustules; in the former the calyx is wider and lower than in the latter. The two species and varieties were not illustrated b}^ Hall, but figures were given with their redescription by Wachsmuth and Springer, and I have figured two. Except for the difference in number of primibrachs, it would be difficult to distinguish this species from Stereocrinus triangulatus of the Michigan area.

THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 43 Out of 45 specimens in my collection, all of which in other respects

THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 45 pentagonal figure within the general basal concavity that is a con-

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Tegmen rather low, subcorneal, smooth or finely pustulose; somewhat depressed or lobed in the interambulacral spaces. The two outer edges are located well below the edge of the arm base and are often broken away. In the broadly concave base, smooth tegmen, and prominent ])innulo openings, tins form is closest to T).

THE FOSSIL CRICOID GENUS DOLATOCRINUS AND ITS ALLIES. 49 The basal star is a most striking and constant character, by which

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A somewhat martian-like form has been observed from western New York, but the material is not available for com-. Ash large to medium in size, occasionally small; elongated hemispheroidal, or depressed bursiform, constricted below the wings; base broadly truncate, flat or shallowly concave.

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The test of the value of such grades in practice emphasizes the importance of abundant material. I have before me the types of 15 of MillerandGurley's species, and besides 31 duplicates in the Gurley collection, and 76 good specimens of my own, of which 62 show the full number of arms, which do. Although this shows a wide range of disturbances in arm development, it will be seen that the variation is mainly within certain limits, approx. 90 percent of the specimens have from 15 to 20 arms, and 50 percent are within one or two of the higher number; so that this ionxi usually has either three or four arms to the ray, the differences being due to the addition or failure of an arm irregularly in one or more rays.

As might be expected, these groups shade into each other in a most confusing way; they are the result of frequent displacements of specimens from one to another without obtaining any result which seems to proclaim their identity by a positive or well-defined and tangible character. In view of the considerable reduction of species which I have felt obliged to undertake, and to avoid too much reliance on my unsubstantiated judgment, I have.

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The more distinctly radiating stripes provide a small basis for separating this from the corporosus form, and the distinction becomes decidedly vague when the intermediate indiansis form is associated with the others. All specimens are large, with flattened tegmen, and the tendency is towards the maximum number. The type included under the above name is the most common form in the current group.

There are about 30 specimens in the collection that probably belong together, ranging in size from 15 to 35 mm. 15 to 18 arms; three^have less than 15; one only 10; the rest have more, up to 20 and one abnormal 22; so that this may be regarded as a typical 15-armed form, as opposed to the approximately 20 arms of the corporosus. Features of note are the generally taller and narrower calyx compared to the corporosus type calyx and the more ventricose tegmen with smoother plates that are rather vaguely defined and tend to develop small spinous nodules.

None of the Miller and Gurley types are good representatives of the adult stage of these fonii, and I have given a figure of the type Wachsmuth and Springer's D. This and the following form are distinguished from the preceding by the fact that they have prominent have nodes and interrupted middle ridges. along the radial series, while differing from each other mainly by the ventricose, lobed tegmen with small thorn tubercles in this species, in contrast to the low, non-thorny tegmen of the following species. Like the latter, except the flat tegmen, without nodes or spines, but sometimes with very small pustules, which can occur on any tegmen classified as smooth.

THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 57 DOLATOCRINUS FUNGIFERUS Rowley

EXPLANATION OF PLATES

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Photographic representation, but little retouched, of an almost complete calyx, showing the contours and surface sculptures, from the deep basal recess (in which the basal recesses are present, although invisible in the shadow, without columns attached to them) to the high rims at the edge leading directly to the free arms. An overlapping transverse fracture interrupts the normal sequence of plates in the upper part, but their arrangement is evident in the right lower sector, where many of the plates are somewhat separated and the suture lines are well marked. Here is a good example of the modified axillary branch, but also of normal size and shape.

Owing to the intricate sculpture, no attempt has been made to outline the plates in the upper part of this figure, although with suitable illumination they can be traced on the specimen in the positions shown in the diagram. The specimen is oriented with the posterior interradius lower right, the small basal, here hidden by the shadow at the bottom of the cavity, is clearly visible in the left anterior position. Surface ornament on cup removed by erosion, but the pits at the corners of the plates, and the lateral ridges along.

Dorsal Adewofa specimen with plates well separated at the sutures, with the modified axillary primibrach in both three- and four-sided forms.

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Tegmen of one of the few known specimens to have parts of wings and pinnae attached; it is embedded and the dorsal parts cannot be seen. 1,2, 3. Basal, lateral and tegmenal views of a typical specimen with .. the most frequent type of surface ornamentation. It shows a large basal pentagonal funnel; iBrj large distally angular with two large fixed setae leading from IIBrj partially to foot; the position and succession of the fixed posts leading from IIBr to the openings at the end of the part between the wings; also .. how the large biserialarm, the distance of two or more biserial pairs of bones, is incorporated into the calyxwall.

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DOLATOCRINUS GRANDIS Miller and Gurley 17.32 2. Part of the stem attached to a large calyx, with nodes in close contact, . and gear-like processes that form continuous ridges. University of Chicago Coll., No. Lateral view of another specimen, showing the typical shape and decoration, and pinule openings close to the edge of the arm bases. ignores Miller and Gurley, with typical surface ornaments and basal pit with pentagonal rim. Figs. ], 2. Basal and lateral views of a smallish specimen, showing the swollen, wrinkled cup plates, smooth tegmen and prominent pinnule openings.

Basal, lateral, and tegmenal views of specimen maximimi showing sharply incised striated or folded ornament, folded tegmen, basalt pit with pentagonal rim, and 20 arms.

EXORNATUS. AND

a 10-arm variant; It is a typical example of the bursiform calyx characteristic of the magnificus group, and of the pustulose style of ornaments of this species, but has only 10 arms. Basal view of the same specimen, with a hexagonal base with a sixth plate aligned with the radials, like the anal plate of the Actinocrinidae.

INDEX