204 



NEW YORK STATE MUSEUM 



c e r a s t r i v o 1 v e [fig. 140, 141], similar to the preceding but 

 more strongly coiled, with similar surface markings, evidently the 

 direct successor of the first species; G. mat her i [fig. 142], 

 like G. trivolve, but with more prominent, distant, irreg- 

 ular, concentric ridges, which are extended about 10 mm beyond 

 the shell, and a symmetric cross section; G. undulatum 

 [fig. 1.43], a closer coiled species than the preceding, with strong, 



Fig. 144 Gyroceras paucinodum 



distant undulations; and G . paucinodu m [fig. 144], like G . 

 undulatum, but with the undulations replaced by nodes 

 along the lateral margins of the coil. 



The trilobites arc represented by Da I m ani t e s (0 d o n t o - 

 c e p h a 1 u s) selenurus [fig. 145], of which the pygidia are 

 most common, and readily recognized by the double prongs of the 

 base, while the cephalon may be known by the anterior crest and 

 the form of the glabella; D . calypso [fig. 140], easily identi- 

 fied by the form of the glabella, short cheek spines, crescentic 

 eyes, and large pygidium rounded at the base, and with an axial 

 row of flattened spines; Lie has (Conolichas) eriopis 



