4 PROCEEDINGS OP THE ACADEMY OP 



width at the two extremities. A similar undescribed species occurs in the 

 " fine-grained sandstone" of Ohio. 



DISCINA, Lamarck. 



Discina patellaris, n. sp. Upper valve circular, elevated, patelliform, 

 with a subcentral beak, from which the surface slopes in right lines to all 

 parts of the margin, except a barely perceptible concavity down the posterior 

 slope. Surface (of cast) with feeble concentric strise. 



Diameter -90 (100); height of upper valve -33 (37); The length appears to 

 be a very little greater than the breadth, but the specimen is slightly defective 

 posteriorly. 



This species recalls D. Alleghania, Hall, of the Chemung Group, but the apex 

 is more central, and the concentric lines less lamellar and regular, and the 

 shell, so far as known, is smaller. 



PRODUCTA, Sowerby. 



Producta ? parvitla, n. sp. Shell very small, semi-elliptic or nearly semi- 

 circular in outline, with a hinge-line equalling the greatest width, or a little 

 less. Ventral valve ventricose, with regular, though slightly diminishing 

 curvature from beak to anterior margin, describing an arc of about 180 ; 

 beak elevated above the hinge-line and incurved over it; flanks regularly 

 convex, abruptly flattened and auriculate at the hinge extremities. Dorsal 

 valve unknown. Surface ornamented with small, rigid, continuous, radiating 

 ribs, which on the sides increase by implantation. 



Length from beak to anterior margin -38 (100); width -31 (82); depth of 

 ventral valve -23 (61). The prevailing dimensions are less than the above. _ 



Amongst Products of similar age the miniature size of the present species 

 renders it at once distinguishable. The specimens look like pygmy examples of 

 P. cora, arcuata or pilciformis. 



Producta Martini, (Sow.) de Kon. (P. sernireticulatus, Martin.) In the wide 

 range of characters admitted into this species, as defined by de Koninck, there 

 is little doubt that the Burlington specimens would be embraced. Although 

 most of the American species of Producta formerly identified with European 

 types have subsequently been separated, P. Martini (or semireliculatus) is still 

 admitted to exist in our coal measures ; and it seems probable that its first ap- 

 pearance dates considerably further back. 



Ranges from the bottom of the Yellow sandstones into the Burlington 

 limestones. 



Producta speciosa, Hall, (Tenth Ann. Rep. Reg. N. Y., p. 176). Several casts 

 of this Chemung species present the appearance of being inside views of very 

 concave dorsal valves ; but no internal structures are visible. The beak is 

 flattened, and not elevated above the hinge-line, which is somewhat shorter 

 than the greatest width of the shell. The other characters also agree. 



STROPHALOSIA, King. 

 Strophalosia ? nummularis, n. sp. Shell of medium size, circular, trunca- 

 ted by the hinge-line. Hinge-line (generally much) shorter than the greatest 

 width of the shell. Ventral valve comparatively very shallow, regularly arch- 

 ing from the anterior side to the vicinity of the beak, which is obtuse, not in- 

 curved and not elevated above the dorsal margin; surface depressed each side 

 of the beak ; area apparently present, but very narrow. Dorsal valve discoid, 

 with abroad, shallow umbonal depression, which is bounded on the two sides 

 by lines diverging from the beak at right angles with each other, or nearly so ; 

 beak depressed, furnished with a small bifid cardinal process or boss, which 

 lies in the plane of the valve and projects beyond the hinge-line ; each branch 

 of the boss continued internally in a low vanishing ridge, which is turned out- 

 wardly into the position of a socket ridge, but without the socket behind it ; 



[Jan.. 



