466 
PALAEONTOLOGY OF NEW-YORK. 
PLATE CX. 
Fig. 2. The exterior surface of a weathered and exfoliated specimen of the left valve. 
Geological position and locality. In the Oriskany sandstone : Albany and Scho¬ 
harie counties (New-York), and Cumberland (Maryland). 
Aifcula recticosta (n.s.). 
Plate CIX. Fig. 3. 
Shell slightly oblique, subrhomboidal : hinge-line greater than the 
greatest width of the shell below; width equal to about once and a 
third the height, very moderately convex. Posterior wing large, ex¬ 
tending nearly as far backwards as the posterior margin of the shell. 
Anterior wing smaller, triangular, slightly concave on the outside. 
Surface marked by strong dichotomizing subequal ribs, which proceed 
principally in pairs from the umbo to the margin of the shell. Posterior 
wing with fine radiating ribs and close concentric laminae; the anterior 
wing being marked only by the concentric striae. 
A single specimen of this species only has been observed, but its form and 
proportions indicate its distinction from the preceding. 
Geological position and locality. In the Oriskany sandstone : Helderberg moun¬ 
tains. 
Plate CX. Fig. 1 a, b ; and Plate CXI. Fig. 2. 
yivicula gebhardi : Conrad, Annual Report on the Palaeontology of New-York, 1841, p. 54. 
Shell “ suborbicular : left valve convex, with about fifteen slightly im- 
“ pressed radiating grooves, forming wide convex obsolete ribs; ears 
“ equal, not produced. Height about five inches.” 
The original specimen, from which Mr. Conrad made his description, is figured 
on Plate cxi. 
PLATE CX. 
Fig. 1 a. A east of the left valve of a specimen. 
Fig. 1 b. A smaller specimen, in which the ribs are better preserved. 
PLATE CXI. 
The cast of the left valve of a large individual of this species. 
Geological position and locality. In the Oriskany sandstone : Albany and Scho¬ 
harie counties. 
