BRACHIOPODA—PROTREMATA. 275 



tension. Surface covered with faint radiating ribs, 3-5 occupying 

 the width of \ inch at the margin. 



Anticosti group of Georgia, and of Anticosti and eastern 

 Canada. 



227. S. castellana White. (Fig. 333.) Siluric. 

 Valves nearly equiconvex, subcircular ; surface of each valve with 



strong, irregularly fasciculate or duplicate plications. 

 Niagaran of Iowa. 



LXVII. Pentamerus Sowerby. 

 Strongly inequivalved, biconvex with highly arched pedicle 

 valve. Like Conchidiutn, but with surface smooth or with but a 

 few broad, obscure, radiating undulations. Siluric. 



228. P. oblongus Sowerby. (Fig. 334.) Siluric. 

 Very large, varying in outline with age. Wider anteriorly. 



Valves strongly convex at beaks. Surface marked only by con- 

 centric lines of growth which are strongest in old shells. The pair 



Fig. 334. Pentamerus oblongus, dorsal and internal views (Pal. N. Y. ). 



of septa in the brachial valve are near together and subparallel. 

 Clinton and Niagaran of New York, Kentucky, Ohio, Indiana, 

 Illinois, Iowa, Wisconsin, Ontario, Anticosti. 



228#. P. oblongus var. subrectus Hall. Siluric. 



Elongate subquadrate ; with high, subrectangular cardinal ex- 

 tremities. Each valve with impressed longitudinal median and 



