850 PALEONTOLOGY OF NEW-YORK. 



Spirifera prteiuatura ( n. s.). 



PLATE XXXIL 



Compare Spiri/er pstudolineatut, Hall, Geology of Iowa, pa. G45, pi. 26, f.4. 1859. 



Compare Spiri/er kirltu, White & Whitfield, Proc. Bost. Nat. llist. Society, Vol viii, p. 293. 1862. 



SuELL transversely oval or suborbicular ; hiuge-line shorter than the 

 width of the shell, with the cardinal angles rounded : surface not 

 plicate. 

 Ventral valve moderately convex, sometimes subventricose,"with a broad 

 and rather shallow sinus, the margins of which are not strongly de- 

 fined : beak moderately elevated and incurved ; area small, the lateral 

 margins undefined. 

 DoKSAL, valve regularly and moderately convex, with a scarcely defined 

 mesial elevation, which becomes broad and more conspicuous towards 

 the front of the shell. 

 Surface marked by numerous regular subimbricating concentric lines, 

 crossed by coarse radiating striaa : these are often continuous, but 

 always more conspicuous on the concentric lines or ridges, sometimes 

 giving a pustulose appearance to the surface. 



The casts or partial casts sometimes preserve the radiating striae more 

 distinctly than the concentric lines. In the perfect shell, the radiating 

 fltriso were doubtless produced from the concentric ridges into minute 

 Bpinules. 



The casts of the ventral valve show the cavities of rather slender but 

 •ometimes considerably elongated dental lamellae. The muscular area is 

 ■omewhat narrow, and only rarely are the parts well defined. There is 

 always a longitudinal impression indicating a median crest or low septum 

 from the apex of the rostral cavity. 



The condition of the specimens is not such as to enable me to give a full ' de- 

 ■cription of the species. They are either casts in fiiable ferruginous sandstone, or 

 partial ca.sts preserving some of the surface markings; while some specimens in a 

 shaly bed have been macerated till the surface characters are obscured. It clearly 

 belongs to the group of Spirifers of which S. lineata is the type, and is closely 



