38 SMITHSONIAN MISCELLANEOUS COLLF.CTIOXS \'()L. 1 03 



in two respects: first, the fixigenes are narrower, and second, the 

 eyes are very mnch larger. 



Surface marked by elongate granules on the elevated portions. 



Name. — KaAi'7rr(o = envelop ; oiJim = eye. 



Genotype. — C. typicalc, new species. 



CALYPTOMMA TYPICALE, new species 

 Plate 12, Figures 8, 9 



The generic description and illustrations present the specific 

 characters. 



Red Lion formation; (loc. i5oe) Boulder Creek, i mile north of 

 Princeton, Montana. 



Holotype. — U.S.N.M. Xo. io<S753a; paratype, No. 108753b. 



ILLAENURUS Hall, 1863 

 ILLAENURUS PRISCUS, new species 



Plate 6, Figtres 3-7 



This species, though not fully typical of Iliac nur us, does not seem 

 to warrant the establishment of a separate genus. The four cranidia 

 figured dififer slightly in proportions, and therefore it is possible that 

 two species are included. Departure from essential features of 

 Illaenurus is found in the great width and faint delimitation of the 

 glabella. Exfoliated specimens show a completely outlined glabella, 

 and a considerable width of fixigene. It has generally been assumed 

 that Illaenurus has no fixigenes, or in other words, that the dorsal 

 furrow passes through the two ends of the e}'e lobe. 



In general outline the cranidium is nearly quadrate. /. priscus has 

 a narrow, wirelike rim, and eyes of moderate size situated about the 

 midpoint of the cranidiuuL Anterior to the eye the facial suture 

 diverges slightly, and the anterior angles are turned down somewhat 

 by a continuation of the cranidial slope. In cross section the glabella 

 has a flat curvature, but longitudinally a much greater one. 



Lyell formation; (Iocs. 66j, k) Ranger Canyon, Sawback Range, 

 Alberta. 



Holotype.— U.S. "^M. No. To8688a; paratypes Nos. 108688b, 

 108689a, b. 



ILLAENURUS ALBERTENSIS, new species 

 Plate 6, Figures 8-12 ; Plate 14, Figure 18 



This species is represented by numerous cranidia, and by a pygidium 

 and libragene. It is not greatly unlike several undescribed species 



