BRACHIOPODA—ORTHIDJE. 



255 



Fig. 304. a-c, Hebertella borealis (Geol. Surv. Canada) ; d, e f H. bellirugosa 

 (Minn. Geol. Surv.) ; /-//, H. occidentalis (Ind. Geol. Surv.). 



175. H. bellirugosa (Conrad). (Fig. 304, d-e.) Ordovicic. 

 Small (less than y 2 inch long), subquadrate. Valves of nearly- 

 equal convexity. Brachial valve with a conspicuous mesial sinus 

 and pedicle valve also at times with a sinus. Surface striae crossed 

 by imbricating lamellae which give the shell a rugose appearance. 



Trenton of Kentucky, Tennes- 

 see, Wisconsin, Minnesota, Iowa. 



176. H. insculpta Hall. (Fig. 



305.) Ordovicic. 



Distinguished from H. belliru- 

 gosa by its larger size (over y 2 

 inch long), more convex brach- 

 ial valve and less prominent 

 concentric growth lines. 



Lorraine of Ohio, Indiana, Illi- 

 nois, Wisconsin, Iowa. 



Fig. 305. 



Heberlella insculpta. 

 Hall.) 



(After 



177. H. occidentalis Hall. (Fig. 304,/-^.) Ordovicic. 



Length and breadth about as 5 to 7. Cardinal area of pedicle 

 valve high ; delthyrium triangular, large and open. Pedicle valve 

 high at beak, depressed into a broad sinus toward the front. 

 Brachial valve regularly and strongly convex with greatly incurved 

 beak which projects slightly beyond the hinge line. Surface 

 marked by elevated, subangular striae crossed by fine concentric 

 growth lines. 



