:;<>s 



some extent, along- the anterior and posterior ends. Valves 

 smooth, oblong, and horny. 



Leperditia hudsonica. Hall. (Fig. 250.) (Pal. X. Y., 

 Vol. III.,. 1859, p. 375.) 



Distinguishing Characters. — Symmet- 

 rical, very convex (sub-globular) form, 

 almost as thick as high; straight dorsal 

 border, with the anterior cardinal angle 

 more developed than the posterior; 

 well-rounded free margins, with anterior 

 extremity less truly rounded than the 

 posterior. 



Found in the Encrinal limestone (?), at "Eighteen Mile 

 Creek, Lake Erie Shore. New York State." (Jones.) 



Fig. 250. Leperditia hud- 

 sonica. Lateral edge and 

 end views of a right valve. 

 x 25 (after Jones). 



Genus jECHIMIXA. Jones and Hole. 



[Ety. : Aichme, a sharp point.] 

 (Ann. and Mag. Nat. Hist., Ser. IV., Vol. III., p. 217.) 



Carapace with thick valves, straight at hinge line, rounded 

 at the ends, and convex at the ventral border. Surface 

 drawn out into a broad-based and sharp-pointed hollow 

 cone, which either involves the whole surface, or rises from 

 the posterio-dorsal or centro-dorsal region. 



JEchimixa marginata. Ulrich. (Fig. 251.) (Joum. Cin. 

 Soc. Nat. Hist., Vol. XIIL, p. 184, PI. XVI.) 



Distinguishing ( 'h a racters . — Small 

 size: elongate form ; narrowed anterior- 

 ly; straight and long dorsal margin. 

 with obtuse angles ; nearly semi-circular 

 free margin, with a slightly elevated 

 marginal rim ; very long and slender 

 spine. 



Found in the "shales of the Hamilton group, in Eighteen 

 Mile Creek, N. Y." (Ulrich.) 



Fifi. 251. A>li i in inn 

 marginata. Left valve, x 

 20 (after Ulrich). 



