BRACHIOPODA—PROTREMATA. 



227 



103. P. sericeus (Sowerby). (Fig. 274, a-b.) Ordovicic-Siluric. 

 Pedicle valve convex in center, deflected at edge. Striae fine, 



FlG. 274, a. Plectambonites sericeus, 

 pedicel valves showing variation. (After 

 Hall.) 



Fig. 274, b. Plectambonites sericeus, 

 exterior dorsal aspect, and interior of pedi- 

 cle and brachial valves, X 2 « (After 

 Hall. ) 



alternating with a few slightly elevated ones and crossed by a few 

 weak concentric ones. Surface shining. 



Trenton-Clinton of New York, Ohio, Kentucky, Indiana, Mis- 

 souri, Wisconsin, Minnesota, Manitoba. 



104. P. transversalis (Wahlenberg). (Fig. 275.) Siluric. 



Pedicle valve very convex, brachial very concave. Hinge line, 



owing to the strongly incurved beak of the pedicle valve, is inflected. 



FlG. 275. Plectambonites transversalis, ventral, dorsal and cardinal views ; and 

 cardinal view of interior of brachial valve. (After Hall.) 



Surface marked by distant and strongly elevated striae with ex- 

 ceedingly fine ones between. The strongly incurved beak of this 

 species is very different from the small beak of P. sericeus which 

 is scarcely distinct from the cardinal margin. 



Clinton-Niagara of New York, Indiana, Wisconsin, Ontario, 

 New Brunswick, Anticosti. 



