PALAEONTOLOGY OF NEW-YOBK. 
Surface marked by eighteen to twenty-two or twenty-three simple 
rounded or rarely subangular plications, two or three of which are 
much smaller and slightly depressed on the middle of each valve, so 
as to form a faint narrow sinus extending nearly or quite to the apex 
of the beaks, and giving a slight emarginate outline to the front. 
Surface marked by line imbricating concentric lines of growth, which 
become strong lamellae towards the margins of the shell : shell granu- 
lose. 
This species differs from the preceding in its more elongate form, larger size of 
full-grown individuals,and less rugose imbricating lines of growth. The plications 
are less strongly developed and more numerous, and the central ones become obso¬ 
lete or nearly disappear before reaching the beak. 
There are rarely individuals, as fig. 2f of Plate xxxvi, which approach more 
nearly in character to the preceding species; but they are always less rotund in 
form, and the beak larger. 
Fig. 2 a - e. Young shells of this species, the plications fine and equal. 
The foramen is represented as extending below the beak, and having a tri¬ 
angular form from the absence of the deltidium : this, however, is an accidental 
condition, as the young shells frequently preserve the deltidium entire, and 
present the round perforation as in the beak of old shells. 
Fig. 2 f. An individual having strong angular strice more like the preceding species, but 
with the elongate form and narrow beak characteristic of this one. 
Fig. 2 g - 1c. Dorsal, profile, and front views of specimens of the ordinary size. 
Fig. 2 l - t. Individuals of larger size and very symmetrical form. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains, Albany county. 
Trematospira deweyi ( n. s.). 
Plate XXXYI. Fig. 3 a - h. 
Wcddheimia deweyi: Descr. of New Species of Pal. Fossils in Regents’ Report for 1856, p. 49. 
Shell depressed subglobose, sometimes subquadrilateral with the sides 
curving : valves nearly equal. Ventral valve a little the most promi¬ 
nent towards tbe umbo, having a narrow faint sinus'from near the 
beak to the front, where it sometimes produces a slight sinuosity : 
beak perforate, extending a little above the opposite beak, upon which 
it is closely incurved. Dorsal valve symmetrically arched, without 
mesial elevation. 
