In an earlier paper (Rasetti, 194S) the author described the Lower Cambrian trilobites occurring in the conglomerate boulders of the lower St. Lawrence Valley, excluding the superfamily rtychopariidea. The present paper completes the description of the fossils of the early Cambrian age. Some species have already been described from material collected by Walcott and preserved in the United States.
This distance is often compared to the width of the glabella, measured at its center. The total width (tr.) of the hind limb is compared with the width (tr.) of the occipital ring. It differs from similar forms mainly in the longer length and more anterior position of the palpebral lobes.
Some of the species discussed here supply information on changes in skull features that occur during growth. Antagmus is mainly characterized by the strong convexity of these distinct cranial parts, the moderate widening of the border, and the divergence of the anterior facial sutures. The writer is more inclined to regard the divergence of the anterior facial sutures as the chief diagnostic feature separating Antagmus from Onchocephalus.
Hind limbs slightly wider (tr.) than nape; marginal furrow broad and deep, reaching distal end of limb.
NO. 7 PTYCHOPARIID TRILOBITES — RASETTI II
12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28
Nevertheless, since the shape of the glabella, the direction of the facial sutures and the structure of the frontal edge are typical of Antagmus, the species can be provisionally placed in this genus. The species was only found associated with an undetermined Onchocephalus and one other undescribed form; therefore the evidence for its Early Cambrian age is not entirely conclusive. Marginal furrow regularly curved or with a slight median bend caused by a widening of the margin.
Palpebral area somewhat convex, horizontal to slightly descending, 0.5 to 0.7 times width of glabella. Palpebral lobes about one-third as long as glabella, level with glabellar midpoint. Posterior limbs about as wide (tr.) as occipital ring, with furrow reaching distal end.
The characteristics of the species attributed to the genus are about average for Lower Cambrian ptychoparians; hence the genus.
14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28
NO. 7 PTYCHOPARIID TRILOBITES — RASETTI 1 5
It appears from the description that this species is intermediate between Eoptychoparia and Onchocephalus, or more precisely between Eoptychoparia normalis and Onchocephalus sulcatus. Frontal area divided into preglabellar field and rim; marginal furrow usually with median inflection. Posterior limbs are broad (tr.) as occipital ring; distal portion narrower (tr.) than proximal portion; marginal furrow reaches distal end of limb.
Anterior facial sutures slightly converging or parallel in front of eyes, then curving inward and rapidly converging; posterior branch curving back towards posterior margin. Forms with less convergent facial sutures and a horizontal palpebral area intergrade with Antagmus or Eoptychoparia; species with a narrower palpebral area approach Crassifimbra; and forms, with a comparatively smaller bond, the clavicle of Luxella. The writer would place in the genus next to the species described by Rasetti (1951) and Lochman (1952), Antagmus soli-
NO. 7 PTYCHOPARIID TRILOBITES — RASETTI 1
The nearest described species is Antagmus solitarius Lochman, which the writer would prefer to place in Onchocephalus because of the slight convergence of the anterior facial sutures. Palpebral area slightly up, 0.6 times wider than glabella; palpebral lobes half as long as glabella, raised; the distance from the posterior end of the palpebral lobe to the posterior margin is less than the length of the palpebral lobe. Anterior facial sutures parallel for short distance between palpebral lobes and marginal furrow; the last branch of the second species of the genus.
This characteristic shape differs from typical species of Onchocephalus in the slightly sloping rather than sloping palpebral area and somewhat longer palpebral lobes. Description.—Glabella straight-sided, moderately truncate in front, sloping down to low front; three pairs of glabellar furrows fairly well impressed. This form corresponds to Onchocephalus in the shape of the glabell and structure of the frontal area, but differs in the slightly oblique palpebral area and the greater length of the palpebral lobes.
Preglabellar field almost disappears medially; border of moderate width (sag.), with barely a trace of a median posterior expansion. Palpebral area decidedly descending, slightly convex, half as wide as glabella; palpebral lobes not preserved, apparently about one-third of glabellar length. Anterior facial sutures slightly converging from eye to marginal furrow; posterior branch as in typical species of Onchocephalus.
This species, intermediate in several features between Onchocephalus and Crassifimbra, is referred to the latter genus because of the narrowness of the palpebral area. It differs from Crassifimbra walcotti (Resser) in the greater relative length of the glabella, deeper dorsal and marginal furrows, raised and narrow border, and granulated surface.
20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28
Luxella is clearly a close relative of Onchocephalus, as evidenced by the intermediate form shown here (Onchocephalus, species undetermined Xo. 3), which shows a widening of the palpebral area, a lengthening of the frontal area, and an increase in the size of the palpebral lobes. . From these features, it is obvious that Luxella is similar to Inglefieldia, Amecephaltis, and Alokisiocare, and may well be in the ancestral lineage of some of these trilobites. Therefore, the species does not refer to Inglefieldia, which is otherwise similar, except for the greater width of the palpebral area.
Description.— Most of the characters of the species have been mentioned in the generic diagnosis and are not repeated. Occipital furrows distinct, occipital ring moderately long (sag.), anterior margin somewhat narrower (sag.) than the preglabellar field medially; marginal furrow is well depressed at the sides, but shallow medially due to a slight posterior extension of the middle portion of the border. Hind limbs appear as wide (tr.) as the occipital ring in dorsal view, actually somewhat longer because the distal, downward portion appears to be shortened.
22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28
7 PTYCHOPARIID TRILOBITES—RASETTI 23 about one-third of the glabellar length, located at the level of the glabellar center. Anterior facial sutures slightly divergent for a short distance before the eyes, bent inward after crossing the marginals in front; anterior portion slightly ventral. The structure of the frontal area and the lesser convexity of the various parts also distinguish Austinvillia from Antagmus, Eoptychoparia and Piasella.
The type species is the only described form that can be assigned to the genus. The furrows of the first, third and fourth pairs start from the dorsal furrow, while the second pair is slightly more inward. Palpebral lobes slightly larger than one-third of the glabellar length; distance from the posterior end of the optic lobe to the posterior margin equal to the length of the optic lobe.
24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128
The border is convex, prominent, swollen medially, narrowed laterally due to the straight course of the marginal furrow and the curved anterior outline of the cranidium. Ocular ridges broad and low on outer surface; palpebral lobes continuous with a shallow^ palpebral sulcus and not strongly raised. The unusually thick testa of this species makes a great difference in the appearance of exfoliated cranidia, where the glabella appears comparatively narrower and the preglabellar field longer (sag.), and all furrows are accentuated.
Description. Most of the features of this species are included in the general diagnosis or are the same as in P.
26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, I28
NO. 7 PTYCHOPARIID TRILOBITES — RASETTI 27
28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28
Palpebral lobes poorly differentiated within the lateral vertical slope, located near the level of the glabellar midpoint (P. yorkensis) or further back (P. roddyi). Anterior facial sutures strongly converging in front of eyes; frontal part somewhat ventral- intramarginal. The posterior branch is first directed inwards, then slightly outwards and inwards again before reaching the rear edge.
The palpebral area is flat and slightly sloping, but does not reach the level of the glabella; optic ridges directed outwards and forwards from the glabella, broad and ill-defined above, turning posteriorly.
30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28
Palpebralarea oblique, narrower than glabella; strong ocular ridges; palpebral lobes one-third as long as glabella, placed obliquely, at level of anterior one-third of glabella. Rimouskia differs from Sao in the less pale, longer glabella, the absence of a distinct sagittal glabellar groove, the straight posterior branch of the facial suture, the stronger and more distal generation of the posterior cephalic margin. Glabellar furrows deeply impressed on lateral thirds of glabella, in some cranidia showing a tendency to connect between various shallow longitudinal extensions of furrows at their inner ends.
Palpebral lobesoblique, one-third as long as glabella, elevated, set off by distinct palpebral furrows; distance from posterior end of palpebral lobe to posterior margin nearly twice as long as length of palpebral lobe.
32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128
EXPLANATION OF PLATES
34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 Plate 3
Dorsal, lateral, and frontal views of the skull, X4 (Peyto Limestone; western edge of Mount Schaffer, Yoho National Park, British Columbia); USNM
