LOWER HELDERBERG ROCKS. * 189 



punctate at their extremities, and appear to be tlie bases of small tubular spines. 

 This chaj-acter, 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 with 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 striae^ 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 tlie 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 rf. Enlargement of part of the dorsal valve, showing the punctate surface, muscular 

 and vascular impressions. 



Fig. 7 «. 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. 



Stropliodoiita leavenwoitliana ( n. s.). 



Plate XXL 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 

 whole valve. Dorsal valve flattened or slightly concave in the umbonial 

 and central regions, very convex and abruptly bent towards the front 



