290 NORTH AMERICAN INDEX FOSSILS. 



264. L. sinuatum Hall. (Fig. 352, //.) Devonic. 

 Differs from L. limitare in its larger size and more robust 



development and in its coarser plications which do not extend to 

 the beak. 



Chemung of New York, Nevada. 



LXXIX. Uncinulus Bayle. 



Subcuboidal with an abrupt anterior slope. Fold and sinus 

 sharply developed only at anterior margin. Plications low, marked 

 anteriorly by a faint median line. Muscular scars of pedicle valve 

 very large and deep. Hinge plate of brachial valve undivided. 

 Cardinal process well developed, bifid or simple. Median septum 

 well developed. Siluric-Devonic. 



A. Plications numerous, about 25 1036 * 



* Median fold rather prominent .1. 



1. Sides and front abruptly deflected , a. 



a. Sinus comparatively narrow 270. U. vellicatas. 



a. Sinus comparatively broad 269. U. abruplus. 



1. Sides and front rounded, not abruptly deflected 265. U. stricklandi. 



* Median fold rounded, not prominent 271. U. nobilis. 



B. Plications few, about 15 to 25 **. 



**Pedicle valve depressed-convex 2. 



2. Brachial valve declining regularly from fiont to beak... 267. U. nncleolalns 

 2. Brachial valve declining more abruptly near the beak. 



266. U. campbellantis. 

 *" Pedicle valve convex 268. U. mutabilis. 



265. XL stricklandi (Sowerby). (Fig. 358.) Siluric. 

 Large (about 1 inch long), ovate very convex. Length and 



breadth about equal. Sides and front rounded. Pedicle valve de- 



pressed-convex ; beak small, closely incurved over that of the 

 opposite valve ; mesial sinus wide, deep in front. Brachial valve 

 gibbous ; mesial fold wide, prominent anteriorly. Surface marked 



