290 



NORTH AMERICAN INDEX FOSSILS. 



or more) curve backward strongly and expand markedly toward 

 the margin. Axis of both thorax and pygidium narrow, about one 

 fifth of entire width. 



Middle Cambric (Stephen formation) of British Columbia. 



XXXIX. AsAPHELLUS Calaway. 



Like Isotehis but hypostoma subcircular with an oval center- 

 piece and posteriorly a very shallow emargination. Cambric. 

 89. A. homfrayi Salter var. macropyga* Grabau and Shimer. 



(Fig. 1598.) Cambric. 



Fig. 1597. 

 (After Walcott.) 



>szs klotzi, X yi' 



Fig. 1598, Asaphellus hovifrayi 

 var. macropyga, broad form of adult. 

 (After Matthew.) 



Cephalon broadly depressed around the margin ; glabella scarcely 

 marked out. This variety differs from the species in the thorax 

 being shorter (not longer) than the pygidium, and the genal spines 

 comparatively long (not very short). (This variety was described 

 but not named by Matthew.) 



Upper Cambric (Bretonian) of Cape Breton. This marks the 

 highest zone of the Atlantic Cambric, equivalent to the Tremadoc 

 of Great Britain. 



XL. AsAPHus Brongniart. 

 Cephalon and pygidium large and nearly equal in 

 Glabella expanded, nearly 



Body oval, 

 size, with broad, infolded margin, 



