412 PROCEEDINGS OP THE ACADEMY OP 



Myalina imbkicaria, n. sp. Shell rather small, very oblique, inflated. 

 Beak (of left valve) compressed, acute, incurved, scarcely rising above the 

 hinge ; posterior margin straight, making a very obtuse angle with the hinge 

 line ; ventral margin regularly curved ; anterior, with a rather deep sinus a 

 little above the middle, and a slight projection in front of the umbo. Hinge 

 line straight, equal to the greatest antero-posterior dimension of the shell. 

 Umbo abruptly convex on both sides, but posteriorly blending with the flat- 

 tened expansion below the hinge. Surface strongly marked by imbricating 

 lamellae. 



Length along the umbonal slope about 1*04 (100) ; this line forms with the 

 hinge line an angle of 29 ; length of hinge line *70 (67) ; angle formed with 

 posterior border 53 ; projection of anterior margin beyond the beak '07 (67). 



Locality. Moscow, Hillsdale county, in the Marshall sandstone. 



This species differs from its analogue M. lamellosa, de Kon. (An. Foss. 126, 

 pi. iii. 6) by its sharper posterior angulation, and deep anterior sinus in the 

 margin. 



Myalina aviccloides. Shell small, obliqne, with subcentral beaks scarcely 

 rising above the straight hinge line. Right valve unknown ; left produced 

 anteriorly just beneath the hinge ; anterior margins parallel, forming an angle 

 of about 70 with the hinge line ; midumbonal slope forming the same angle, 

 having its anterior declivity convex, its posterior at first convex, then slightly 

 excavated, giving an extended appearance to the posterior margin, but with- 

 out any perceptible isolation of a posterior wing ; ventral margin regularly 

 curved. Surface marked by faint incremental lines. 



Length along umbonal slope *34 (100) ; length of hinge line -31 (91) ; 

 greatest antero-posterior dimension "32 (94). 



Locality. Marshall. 



Myalina pterine;eformis, n. sp. Shell small, equivalve, obliquely elongate, 

 with an alate posterior expansion, which is suddenly thickened above to form 

 the basis of the straight elongated hinge line. Beaks subterminal, obtuse, 

 incurved, elevated a little above the hinge ; midumbonal slope making an 

 angle of about 35 with the dorsal margin ; from the upper portion the de- 

 clivity is steep to the hinge on the posterior side, while on the anterior side 

 the shell swells out into a sort of pouch, projecting beyond the beak ; poste- 

 rior margin of shell showing a sinuation just below the hinge, from which a 

 regular curve sweeps around to the anterior side. Shell thin, with fine in- 

 cremental lines. 



Length of shell along dorsal margin *44 (100) ; length from beak along 

 midumbonal slope - 38 (86) ; distance from beak to anterior extremity, 

 10 (22) ; to posterior -34 (78); diameter of shell through umbo '12 (24). 



Locality. Pt. aux Barques, from a friable and ferruginous sandstone over- 

 lying the grindstones. 



Fterinea, Goldfuss. 



Pterinea cardinata, n. sp. Shell . c mall, hinge line extremely elongate, 

 posteriorly terminating in an angle of 40, separated by a slight sinuation 

 from the body of the shell ; ventral margin transversely semi-elliptic ; ante- 

 rior wing short, saccate ; anterior margin forming with dorsal line an angle 

 of about 45. Beak flattened, not elevated above the hinge ; umbonal slope 

 terminating at the middle of the ventral border, opposite which is the greatest 

 width of the shell ; descent from the umbonal slope to the antero-ventral bor- 

 der very abrupt. Surface of cast showing numerous faint concentric grooves 

 which are most conspicuous in the postumbonal region. 



Length of hinge "65 (100) ; greatest width of shell '21 (32) ; convexity of 

 right valve *06 (9) ; length of anterior wing -06 (9). 



Locality. Grindstone quarry, Pt. aux Barques, with Rhynchonella cameri- 

 ftra, &c. 



[Sept. 



