CORALLINE LIMESTONE. 



331 



691. 11. AVICULA? ■ sp. 



PL. LXXV. Fig. 2 a, b, c. 



Equivalve 1 extremely convex along the middle obliquely backwards ; anterior wing short ; 

 posterior one not separated from the body of the shell by any distinct sinus. 



A single imperfect specimen only has fallen under my observation ; and this being a cast, 

 without external markings, it is impossible to characterize the species satisfactorily. 



Fig. 2 a, h, c. Right and left valve, and profile view of the specimen. 



Position and locality. In the Coralline limestone at Schohaiie. 



{Collection of JouN Gebhard junior.) 



. , ' 692. 12. AVICULA SUBRECTA (n. sp.), 



Pl. LXXV. Fig. 3. 



Shell slightly oblique, gradually expanding from the beak ; anterior wing short, triangular ; 

 posterior wing wide, triangular, separated from the shell by a subdefined sinus ; surface finely 

 striated ; striae crossed by obscure concentric lines of growth. 



The single specimen examined is not well preserved, though the general form and surface 

 markings can be determined. The posterior wing is imperfect along the hinge line, as well as 

 on the outer margin. It is clearly a distinct species from any shell previously described from 

 our strata, and, so far as known, is restricted to the thin mass in which this specimen has been 

 found. 



Fig. 3. Left valve of A. subrecla. 



Position and locality. In the Coralline limestone at Schoharie. 



{Collection of John Gebhard junior.) 



693. 13. AVICULA SECURIFORMIS (n. sp.). 



Pl. LXXV. Fig. 4, 5 a, and 5 fe. 



Shell wide (width nearly one-sixth greater than the height), subrhomboidal, oblique ; an- 

 terior wing scarcely existing ; posterior wing narrow and small j posterior margin of the shell 

 extending more than one-fourth of the width beyond the extremity of the wing ; surface of the 

 cast (fig. 4) marked by concentric lines of growth, and on the margin with faint impressions 

 of radiating striae. 



The specimens 4,5 a and 5 b appear all to belong to the same species ; the former being a 



cast of the interior of the left valve, while the two other figures show the interior of the same 



valve in specimens of different size. The central part of the cast is roughened from weathering, 



and whatever markings there may have been upon it are obliterated. Towards the margin, 



[Palaeontology — Vol. ii.] 42 



