426 



NORTH AMERICAN INDEX FOSSILS. 



172. L. rogersi Hall. (Fig. 556, b.) Devonic. 

 Umbonal region gibbous. Posterior ear with mucronate ex- 

 tremity. 



Hamilton : New York, Pennsylvania, Iowa. 



173. L. sociale Hall. (Fig. 556, c.) Devonic. 

 Distinguished by its form and regular lamellose appearance of 



the surface. 



Chemung : New York. 



174. L. maclurii Hall. (Fig. 556, a.) Devonic. 

 Body of shell gibbous, oblique. Anterior ear limited by a broad, 



vertical furrow. 



Chemung : New York, Pennsylvania. 



Fig. 556. a, Leptodesma maclurii, left valve; b, L. rogersi; c, L. sociale; d, e, 

 Lunulicardium curium, right and left valves; f-i, Pterochcenia fragilis ; j, Lunuli- 

 cardium acutirostrum, left valve. (Pal. N. Y., V.) 



L. Loxopteria Freeh. 

 Inequivalve, very inequilateral. Anterior muscle scar small. 

 Ligament external. Teeth obscure. 



Appearance like the gastropod Capalus. Left valve very con- 



