288 NORTH AMERICAN INDEX FOSSILS. 



Pleural grooves extending nearly to the end. Pygidium more 

 strongly segmented than in B. productus, and pleural grooves more 

 extended. 



Middle Cambric of Nevada and British Columbia. 

 8i. B. rotundatus Rominger. (Fig. 1593.) Cambric. 



Differs especially from B. howelli in its narrower form, more 

 arched palpebral lobes, different facial suture, nine thoracic seg- 

 ments, and the pygidium much longer, with axis and segmentation 

 reaching its margin. 



Middle Cambric of British Columbia. 



XXXVI. Bathyurus Billings. 



Differs from Bathyuriscus in the very obscure furrows of its 

 subcylindrical glabella, and in the more strongly convex pygidium, 

 with its longer axis and narrower border. Ordovicic. 



82. B. conicus Billings. Ordovicic. 

 Glabella conical, narrowing forward, with a deep furrow all 



around. Surface covered with tubercles. Cephalon, at least an- 

 teriorly, bordered by a furrow. Length of cephalon 5/s inch. 

 Beekmantownian of Champlain Valley and Canadian extension. 



83. B. amplimarginatus Billings. Ordovicic. 

 Differs from B. extans in the broad smooth margin of the py- 

 gidium. 



Beekmantown of Mingen Islands, and of Pennsylvania, etc. 



84. B. extans Hall. (Fig. 1594.) Ordovicic. 

 Very convex. Pygidium with a prominent axis and a thickened 



margin. (Type of genus.) 



Lowville and Black River of New York and Minnesota; Upper 

 Stones River and Trenton of Wisconsin and Quebec. 



85. B. smithi Billings. (Fig. 1595.) Ordovicic. 

 Minute. Glabella strongly convex, the most so in the middle. 



Dorsal and neck furrows deep; frontal margin obtusely rounded. 

 Black River of Ontario. 



86. B. spiniger Hall. Ordovicic. 

 Differs from B. extans in its broader frontal border, in the 



presence of an occipital spine, and in its tuberculate glabella. 

 Trdnton of New York, 111. and Quebec; Lowville of Kentucky. 



