240 



NORTH AMERICAN INDEX FOSSILS. 



the umbo. 



137. S. truncata (Hall). (Fig. 292.) Devonic. 



Small. Pedicle valve gibbous, regularly arched and truncated at 

 Cardinal extremities flattened and auriculate. Brachial 

 valve gently concave. Surface of 

 both valves covered with scattered 

 spines. 



Hamilton, Portage and Ithaca of 

 New York, Nevada, Ontario. 



XLVI. Productella Hall. 



Fig. 292. Strophalosia truncata. 



(After Hall ) Productoid. Small, with straight 



hinge line and narrow cardinal areas. 

 Pedicle valve strongly convex and produced anteriorly, with 

 overarching beak; deltidium present; teeth small. Brachial 

 valve small, concave; cardinal process usually bilobed. Surface 

 marked by radiating ridges which bear spines at intervals. Differs 

 from Strophalosia also in the lack of umbonal attachment. De- 

 vonic-Carbonic. 



A. Spines numerous *. 



* Length much greater than breadth 138. P. navicella. 



* Length and breadth about equal I. 



I. Spines arranged in concentric rows 142. P. speciosa. 



I. Spines irregularly scattered ., a. 



a. Brachial valve moderately concave I / . 



i / . Lamellose growth lines present... 144. P. pyxidata. 



i'. Lamellose growth lines not present 145. P. shumardana. 



a. Brachial valve very concave 2 / . 



2 / . Cardinal margins conspicuously flattened... 139. P. spinulicosta. 

 2 / . Cardinal margins not conspicuously flattened. 



146. P. concentrica. 



B. Spines few and scattered **. 



** Length much greater than breadth, radiating striae coarse. 



143. P. arcuata. 



** Length and breadth about equal, radiating striae fine 141. P. hallana. 



** Length much less than breadth 140. P. subalata. 



138. P. navicella Hall. (Fig. 293, a-b.) Devonic. 



Small ; length much exceeding width. Hinge line less than 



a c d b 



Fig. 293. a, b, Productella navicella; c, d, P. spinulicosta. (After Hall.) 



