40 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



in which the valves are normally folded (uniplicate), but a third 

 specimen has a wider sulcus on the pedicle valve which shows a 

 definite twist. This species has abbreviated dental plates and the 

 same cardinalia as the Italian forms and 5. streptimorpha. 



STREPTARIA STREPTIMORPHA Cooper, new species 

 Plate 19, B 



Of medium size for a rhynchonelloid, subcircular in outline; sides 

 narrowly rounded ; greatest width at the middle ; anterior commissure 

 twisted. Surface marked only by concentric growth lines. 



Pedicle valve gently convex in lateral profile ; broadly and slightly 

 convex in anterior profile; depth less than that of the brachial valve; 

 umbonal and median regions slightly swollen ; sulcus indefinite, shal- 

 low ; beak short, blunt, forming an obtuse angle (about no°). 

 Foramen hypothyrid, small, oval ; deltidial plates forming low rim 

 around foramen. 



Brachial valve deeper than the pedicle valve, moderately convex 

 in lateral profile but strongly domed in anterior profile; umbonal 

 region somewhat flattened ; median region and flanks strongly swol- 

 len ; fold ill defined because of twisted commissure. 



Interior. — Pedicle valve with remnantal deltidial plates and no 

 pedicle collar. Brachial valve with long falciform crura attached to 

 the socket ridges by fairly broad outer hinge plates. Median septum 

 absent. Other details not yet known. 



MEASUREMENTS IN MILLIMETERS 

 Length 



Holotype 17.0 



Types.— Holotype, U.S.N.M. 549386a; figured paratype, U.S.N.M. 

 549386b. 



Horizon and locality. — Eocene, deep cut north of Grua 9, Ramal 

 Juan Criollo, Camaguey Province, Cuba (Palmer locality 1640). 



Discussion. — This species is characterized by its rounded form, 

 small foramen, and broadly twisted anterior commissure. It is sug- 

 gestive of Streptaria de bitchii (Michelotti) from the Mediterranean 

 region but differs in its rounded form, less narrow twist to the an- 

 terior commissure, smaller foramen, and lesser development of the 

 foraminal lip. 



