LOWER HELDERBERG ROCKS. 817 



Surface marked by about forty regular simple rounded striae, which are 

 crossed by indistinct lines of growth, and, near the front, by a few 

 stronger imbricating concentric marks indicating interrupted stages of 

 growth : shell granulose. 

 This shell has the general form of Jitrypa reticularis; but the surface is marked 



by fine regular simple striae, two or more of those occupying the mesial sinus of the 



ventral valve becoming obsolete before reaching the beak. 



Fig. 3 a, b, c, d. Dorsal, ventral, profile, and front^ views of a very perfect specimen of 

 medium size. 



Fig. 3 e, f, g. Ventral, dorsal, and profile views of a larger specimen, the sides of which 

 slope more rapidly from the beak. 



The entire collections made during a period of fourteen years have yielded 

 but ten individuals of this species. 



Geological position and locality. In tlie shaly limestone of the Lower Helderberg 

 ^oup . : Helderberg mountains, Albany county. 



Treinatospira rectirostra (n. s.)- 



Plate XXXVI A. Fig. 1. 

 Waldheimia reetirostra : Descr. of New Species of Pal. Fossils in Regents' Report for 1856, p. 49. 



Shell longitudinally ovate, tapering towards the beak, slopes on each 

 side of the beaks, flattened and not plicated. Beak of ventral valve 

 straight, extending much beyond the opposite, truncated at the apex 

 by a round perforation, which is partly limited by the deltidium : 

 beak of dorsal valve incurved, and penetrating the opposite valve. 

 Surface marked by twelve or thirteen prominent subangular plications, 

 the two central of which, on the ventral valve, are slightly smaller 

 than the others, and a little depressed. These two plications coalesce 

 before reaching the beak : the central plication of the dorsal valve is 

 smaller and a little more depressed than the others, and becomes 

 obsolete before reaching the beak. 



This well-marked species may be at once distinguished from either of the pre- 

 ceding by its less ventricose form, and the more attenuated and straight beak of 

 the ventral valve. 



Fig. 1 a, b, e. Dorsal, ventral, and profile views. 

 Fig. 1 d. Cardinal view, showing the foramen. 

 Geological position and locality. Oriskany sandstone, Maryland, 

 f Pai,.«!Ontology III.] 28 



