LOWER HELDERBERG ROCKS. 
18® 
punctate at their extremities, and appear to be the bases of small tubular spines. 
This character, however, is very variable, and in some specimens obscure upon the 
surface of the shell, while it becomes conspicuous on the exfoliate specimens, and 
the casts are strongly punctate, while the interior of the shell is distinctly pustu- 
lose. 
This species has the form of S. englypha of the European rocks, and has been 
considered as identical w T ith that species. I find, also, that Mr. Conrad, in his cata¬ 
logue of species in Report of 1841, has omitted S. punctulifera and cited S. englypha. 
Specimens of S. englypha from Gothland, with a very similar form, have 'strong 
angular strise, between which are fascicles of three, four, five, or six smaller ones; 
a character not observed in the New-York specimens. The punctse are finer in the 
European specimens than in ours, and the general aspect of the shell less rude. Our 
specimens are, for the most part, in such a condition as to afford very unsatisfactory 
material for illustration. 
PLATE XXI. 
Fig. 4 a. A cast of this species. 
PLATE XXIII. 
Fig. 4 a, b. The interior and profile view of the dorsal valve. 
Fig. 5 c. Cardinal view, showing the area enlarged. 
Fig. 6 d. Enlargement of part off the dorsal valve, showing the punctate surface, muscular 
and vascular impressions. 
Fig. 7 e. Enlargement of striae which are scarcely exfoliated, showing pustulose points, 
some of which are punctate at their extremities. 
Geological position and locality. In the Pentamerus limestone and shaly limestone 
of the Lower Helderberg group : Helderberg mountains ; Schoharie, Carlisle, 
Hudson, Catskill; Columbia, Herkimer county, etc. 
Strophodonta leavenwortliana ( n. s.). 
Plate XXI. Fig. 5 - 7; and Plate XXIII. Fig. 1-3. 
Shell semielliptical, about three-fourths as long as wide, contracted below 
the extremities of the hinge : cardinal border slightly sloping from 
the beak. Ventral valve convex at the umbo, flattened in the middle 
and on the cardinal margins, so as to form a semicircular inclined plane 
ascending from the hinge to beyond the middle of the shell; the front 
and lateral margins abruptly inflected, giving a deep concavity to the 
wliole valve. Dorsal valve flattened or slightly concave in the umbonial 
and central regions, very convex and abruptly bent towards the front 
