In the course of this research many interesting facts have come to light, and it is becoming clear that a large part of paleontology is. Care has been taken to ensure strict compliance with the rules of the International Commission of Zoological Nomes. Border with a well-defined border of approximately one-third the width of the preglabellar area; the rim thickened and extended forward into a blunt spine medially.
Cheeks fixed semi-laterally like glabella: palpebral lobes strongly curved, raised and entirely beyond the rather straight course of the facial suture. The facial suture diverges slightly before the eyes and is intramarginal for perhaps one-third of the distance from the center. It is not entirely certain that this species can remain in Alokistocare due to the narrow cranidium, but without the additional spicule.
DESCRIBED SPECIES REFERRED TO ASAPHISCUS
As Shumard's types were not illustrated and were later destroyed by fire, the appropriateness of recognizing his species may be questioned, but Walcott long ago disregarded the specimens as the species. As the genus is described herein, the species fall into two groups: those with two marginal spines seated at the anterior corners of the pygidium; and the typical group which lacks them. As far as all other characters seem to agree, this feature is not considered to have generic value.
DESCRIBED SPECIES REFERRED TO BATHYURISCUS
The published illustrations do not accurately show the full length or direction of the spines, which turn back and reach the rear end of the shaft. Fixed cheeks rather broad and rising from the dorsal sulcus to the palpebral angular lobes. Comparisons.—Superficially, Billingsaspis resembles Bolaspis, except for the depression where the latter has the chief boss in the pre-glabellar area.
This undoubtedly deserves a full generic rank; in fact, it is doubtful whether it is even closely related to Asaphiscus. A fairly large group of Cambrian trilobites, commonly called Acrocephalites and Alokistocare because of the highly developed boss in the center of the preglabellar field, has long needed a common name. Diagnosis. Cranidium characterized by a conical glabella, with one or more pairs of rather sharply reflected grooves; firm cheeks broad and swollen; eyes small and sometimes stalked; large round or tri-.
Comparisons. When Acrocephalites was first described from fragmentary specimens, which fail to provide a correct concept of the genus, the conical glabella and boss in the preglabellar region were the only visible general features. Comparing Bolaspis to Alokistocare, we find little similarity, except in the possession of the mid-boss. Moreover, the dorsal grooves are shallower and the fixed cheeks less high, so that the entire skull is fairly uniformly convex in cross-section.
This specimen clearly had a large occipital spine and not just a thickened neck ring as pictured. This genus differs from others in the group previously mentioned as Bathyuriscus in having a faster-growing glabella in front of the eyes and in having a large tail in which the pleural furrows reach the margin and increase in width towards their extremities.
DESCRIBED SPECIES REFERRED TO CLAVASPIDELLA Poulsen described three species
Some Upper Cambrian forms previously mentioned in Acrocephalia may be descendants of Middle Cambrian forms, but are generally distinct. Glabella pale, rather conical, somewhat more than half of cranidium; no glabellar furrows visible in available specimens. Lip wide with a narrow rim of preglabellar area of equal width, traversed by median vertical ridge, starting from dorsal furrow and widening to join lip.
Eye lines strong palpebral lobes small, located a little behind the center of the cranium. Comparisons.— Compared with the somewhat older species of Alokistocarc and Acrocephalops, this genus resembles both in certain features. Features of the rim as well as the middle rim, which re- ])laces the boss, distinguish it from Acrocephalops, and the less extended rim and the well-defined rim separate it from Alokistocare.
DESCRIBED SPECIES REFERRED TO DEIRACEPHALUS
Comparisons.— Compared with the somewhat older species of Alokistocarc and Acrocephalops, this genus resembles both in some features. The features of the margin and the median ridge replacing the ridge separate it from Acrocephalops, while the less expanded margin and well-defined margin separate it from Alokistocara. The following list shows the generic position of the North American forms which do not belong to the Atlantic Province.
DESCRIBED SPECIES REFERRED TO DUNDERBERGIA
Upper Cambrian, Wilberns; (loc. 70) Baldy Mountain, near Morgans Creek, 8 miles NW of Burnet, Texas. Ehman, of Logan, Montana, who has contributed material to the resurvey of the classic region along the north side of the Gallatin Valley. The pleural lobes are very distinct because both the pleural furrows and the furrows are distinctly impressed to the margin.
Unfortunately, this species is not illustrated, and it is necessary to limit it to one of the three or more species found in the type lot. Middle Cambrian, Meagher; (loc. I5id) south of Gallatin River, Crowfoot Ridge, Yellowstone National Park, Wyoming. Another group previously referred to Alokistocare deserves a separate generic name, and as it appears to reach its best development in the Eldorado Limestone of Eureka County, Nevada.
Diagnosis.— Cranidium generally rectangular in outline, with a tapering glabella about half as long as the cranidium; usually well defined by shallow dorsal furrows; glabellar pore faint or absent. Margin broad, usually with a large median bush; margin not sharply separated due to the poor development of the anterior furrow. Comparisons.- Compared to Bolaspis and Acrocephalops, this genus lies between the two but closer to the former.
Species have already been incorrectly named to Elrathia, as they were previously to Ptychoparia, so great care must be taken to prevent this name from becoming a "dump" as well. These forms have the so-called "median" trilobite structure, so many genera are close to each other.
ADDITIONAL SPECIES REFERRED TO ELRATHIA
28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 Elrathia haguei (Hall and Whitfield)
ADDITIONAL SPECIES REFERRED TO EUREKIA Eurekia denticulata (Meek)
Free cheeks rather broad with a broad border when the broad doubling is pressed on them, otherwise sloping smoothly to the margin. Axial furrows often faint; pleural furrows weak but clearly traceable in some species to outer margin; wide rim sometimes determined when doublure is impressed on test. Comparisons.—Glossoplenra, as pointed out by Poulsen, resembles Anoria in the number of thoracic segments and the prolongation of the glabellato anterior margin, but differs in having longer eyes.
From the other members of the family Glossoplenraitis it is distinguished by its less developed furrows, the absence of a ridge on the cephalon, and the large size and posterior position of the eyes.
DESCRIBED SPECIES REFERRED TO GLOSSOPLEURA
There is some hesitation in placing this form in Glossopleura, but the pygidium is completely typical as areal, as well as the eyes and palpebral lobes. Compared to G.prodiicta, this species has a larger glabella, which expands forward somewhat faster and the pygidium lacks the pleural furrows and has much weaker axial furrows. Comparisons.— As stated by Poulsen, this genus differs from Asaphisais in having genital spines, long-pointed pleura, and a broad, advanced pygidium, the pleural furrows of which are continued into the concave border.
Middle Cambrian, Meagher; (loc. 5f) 11 miles south of Neihart and Dry Creek, East Gallatin River, Montana.
IDAHOIA WALCOTT, 1924
ADDITIONAL SPECIES REFERRED TO IDAHOIA
36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 Idahoia hera (Walcott)
DESCRIBED SPECIES REFERRED TO KOCHASPIS Kochaspis liliana (Walcott)
Middle Cambrian, Gordon Mountain; (loc. 150b) Chinese Wall, South Fork, White River-Indian Creek Pass, Montana. We are dealing here with a group of trilobites which developed greatly in the late Lower Cambrian and continued into the Middle Cambrian. Because of the width of the fixed cheeks, some species were referred to Olenopsis, while those for which the pygidium was known were placed in Crepicephalus.
DESCRIBED SPECIES REFERRED TO KOCHIELLA
Wide fixed cheeks, heavy eye lines; eyes of moderate size and set far apart. The free cheeks are greatly expanded at the genital angles, flat or concave on the outside, and with long, broad genital spines. Diagnosis.— Cranidiumquadrate, the facial sutures diverging before the eye, making sharp, prominent, downward-turning anterior angles; postero-lateral limbs short.
Pygidium spade-shaped with anterior pleural furrows forming upturned sides; dorsal sulcus marked only by a change in slope; lack of axial and pleural; axis tapering rapidly, half as long as pygidium. Margin about one-third as wide as long glabella; heavy, thickened, upturned margin separated by a strong anterior furrow; the preglacial area is almost obsolete in the anterior part of the glabela. Variety A and other specimens assigned to the species appear to be similar except for size.
This specimen is typical of the genus Modpcia, deviating only in mid-boss development. Solid cheeks about half the width of the glabella; eyes small, located opposite the anterior third of the glabella. Apparently Walcott first intended to use the Pole Creek form, Bathyuriscus potversi, as the genotype, but since he designated the Spence shale form, it becomes the genotype, and the genus is not represented at the Pole Creek site.
Diagnosis. Cephalon much larger than pygidium, extended anteriorly; two pairs of glabellar grooves, usually well defined, others very weak or absent. Pygidium with broad, well-defined axis; pleura usually fused; two . four pleural grooves extend to the margin; edge absent.
DESCRIBED SPECIES REFERRED TO POLIELLA
Comparisons.—Compared to Bathyuriscus, Poliella is distinguished by its fewer thoracic segments, larger eyes, and much smaller. tail. Due to the poor preservation of the holotype, this species would be inadequately represented except for two excellent shields. Facial suture diverges anteriorly to rather sharp anterior angles; glabella tapering with faint furrows; occipital furrow shallow; occipital ring slightly thickened.
Margin broad, concave and borderless, striated vertically; eye lines developed; palpebral lobes of moderate size, located far back. Two species from the Upper Cambrian in the house series, referred to the Middle Cambrian genus Asaphiscus, differ in many. Facial suture diverges anterior to the eyes and is intramarginal two-thirds of the distance to the middle, so that the anterior angles are strongly rounded.
Border of medium width; the edge became thicker and, as a result of the suture, sharply narrowed towards the front corners. Pygidium half the size of the cephalon; axis well defined, quite broad and reaching almost to the edge; distinguish axial and pleural grooves.
