196 



NORTH AMERICAN INDEX FOSSILS. 



f — k 



Fig. 229. a, Westonia ella, X 2 ; b, mold of interior of dorsal valve, \ 2 ; c, Lin- 

 %ula elderi, dorsal view, X l '■> d, L, ligea, X 2 > e, L. ??iodesta, X 4 '■> f g h> L. iowaen- 

 sis ; dorsal and profile views, and mold of interior of ventral valve, X * > i ji L. eva, 

 dorsal and profile views, X * » k, L. umbonala, X I- (After Walcott (a, d), Win- 

 chell and Schuchert, and Ind. Surv. (/£).) 



21. L. eva Billings. (Fig. 229, i-j.) Ordovicic. 

 Widest near the front, with nearly straight gradually converg- 

 ing sides; valves convex, flattened near front; surface with a few 

 prominent radiating striae on anterior half. 



Black River of Canada, Minnesota, etc. 



22. L. elderi Whitfield. (Figs. 221, 229, r.) Ordovicic. 

 Subquadrangular with nearly parallel margins and subequal ex- 

 tremities, the beak being somewhat angular and the front broadly 

 rounded. Valves quite convex. The dorsal or shorter and more 

 convex valve marked by a flattening along the middle. Surface 

 nearly smooth. 



Trenton and Lorraine of Ohio, Wisconsin, Minnesota. 



23. L. modesta E. O. Ulrich (Fig. 229, e.) Ordovicic. 

 Minute, subovate; widest anteriorly. Valves nearly flat. An- 

 terior third uniformly rounded. Surface marked with very faint 

 concentric undulations. 



Trenton-Lorraine of Iowa, Kentucky, Minnesota. 



24. L. iowaensis Owen. (Fig. 229,/, g y h.) Ordovicic. 

 Large, broadly subquadrate, generally a little narrower above 



the middle than below. Beak obscurely angular, front rounded. 

 Sides gently rounded. Valves convex. Beak of pedicle valve 

 projecting a little beyond that of the brachial and more pointed. 

 Surface marked by strong and irregular growth lines. 



Galena of Iowa, Illinois, Wisconsin, Minnesota, Manitoba. 



