LOWER HELDERBERG ROCKS. 
217 
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 Atrypa reticularis ; but the surface is marked 
by fine regular simple strise, two or more of those occupying the mesial sinus of the 
ventral valve becoming obsolete before reaching the beak. 
Fig. 3 a, b, e, d. Dorsal, ventral, profile, and front views of a very perfect specimen of 
medium size. 
Fig. 3 c, 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 the shaly limestone of the Lower Helderberg 
group : Helderberg mountains, Albany county. 
Trematospira rectirostra (n. s.). 
Plate XXXVI A. Fig. 1. 
Waldheimia redirostra : 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, c. Dorsal, ventral, and profile views. 
Fig. 1 d. Cardinal view, showing the foramen. 
Geological position and locality. Oriskany sandstone, Maryland. 
[ Paleontology III.] 28 
