146 PALEONTOLOGY OF NEW YORK. 



anterior instead of posterior bend at its junction with the lateral branches, and 

 each of these branches bears a single row of irregular, somewhat ramose pro- 

 cesses directed toward the inner edges of the umbonal blades. What the sig- 

 nificance of these processes may be is not evident from a study of the specimen. 

 They do not appear to be of mechanical origin or due to crystallization of silica 

 upon the lamellse, but may possibly indicate a pathological or excresential 

 condition. 



Fig. 13.'. 

 Loop of Nucleoxpira, sp. ?, from the Cornilerous limestone at the Falls of the Ohio. (c ) 



Genus CYCLOSPIRA, gen. nov. 



PLATE LV. 



1842. Orthis, Emmons. Geology of New York; Rejjt. Second Dist., p. 395, fig. 4. 

 1847. Atrypa, Hall. Palseontulogy of New York, vol. i, p. 139, pi. xxxiii, figs. 3 a-e. 



This proposed division is founded on the species, Orthis bisulcata, Emmons 

 {Atrypa bisulcata. Hall), of the Trenton limestone, which in external characters 

 is very similar to the Dayia navicula, Sowerby, of the Wenlock fauna. It is 

 indeed surprising to find that two species so nearly alike externally, should 

 differ so essentially in internal features as to require their separation into 

 groups which appear but remotely related. 



Atrypa bisulcata is a subtrihedral shell with a very convex pedicle-valve and 

 a depressed brachial valve. The larger valve has a prominent umbo, the 

 beak being closely incurved over the hinge, concealing both foramen and 

 deltidium. The umbo is longitudinally keeled, but at about one-third the 



