222 TWENTT-FOVRTH REPORT ON THE StATE MuSEUM. 



vex above the middle ; the beak pointed and projecting considerably 

 beyond the opposite valve ; with a depressed or concave triangular 

 area. Interior of the dorsal valve marked near the middle by two com- 

 paratively large semicircular or reniform muscular scars, the breadth 

 across the two more than equal to one-third of the diameter of the 

 valve : the center of the valve has also a slight mesial septum. 



Surface strongly punctate in concentric curves passing from the 

 center of the shell outwards, extending through the shell near the 

 front of the valves, and distinctly marking the cast : inner layers of 

 shell not punctate. 



Specimens of this species have been sent from Cincinnati, and pub- 

 lished and figured as the T. terininalis of Emmons. It differs from 

 that species, however, in being more transverse, with a less convexity 

 of the ventral valve and more prominent beak of the dorsal valve ; 

 and also in the character of the punctate structure. The Trenton 

 species is distinctl}^ punctured, the puncta passing through the shell, 

 showing most distinctly on partially exfoliated specimens ; while in' 

 this species they are entirely confined to the exterior layers of the 

 shell. It is also destitute of the radiating strige always found on T. 

 terininalis when the sliell is partially exfoliated. 



The specimens of this species usually measure about half an inch 

 in length and five-eighths of an inch in width. I have received 

 them from Mr. S. P. Carley, Mr. U. P. James, and other sources. . 



Formation and locality. In shales of the Hudson-river group, 

 Cincinnati, Ohio. 



TeEMATIS ? PIJSTTJLOSA U. Sp. 



Shell large, subquadrangular, both valves strongly convex; the 

 greatest convexity of the ventral valve at or below the middle ; that 

 of the dorsal valve, above the middle. Peduncular opening small, 

 near the cardinal margin. Beak of the dorsal valve not prominent. 



Surface marked by concentric wrinkles and fine distant radiating 

 striae, which are produced in pustules or short spines on the front of 

 the valves, where they cross the concentric lines, and become trans- 

 verse nodes on the lateral portions of the shell. 



In casts, or much exfoliated shells, there are radiating lines, which 

 appear to have been vascular markings. 



This species is easily distinguished by its subequally ventricose 

 valves, the quadrate outline, and the peculiar surface-markings. 



The length of the specimen is about three-fourths of an inch with 

 a width of a little more than one inch ; the depth of the two 

 valves together is about five-eighths of an inch. 



Formation and locality. In shales of the Hudson-river group, 

 three miles east of Horicon, Wisconsin. 



