124 Carl O. Dunbar, 



Dorsal muscle-scars similar to those of D. suhcarinata, but more 

 slender. Surface covered by coarse fasciculated striae, of which 

 about thirteen occupy a space of 5 mm. at the margin. 



Dimensions: Length, 15 mm.; width, 17 mm.; depth, 6 mm. 



Discussion: In outline and carination this shell closely resem- 

 bles D: suhcarinata, but in comparison with that species it is 

 more coarsely striated, has a more emacerated appearance, the 

 dorsal valve being concave in the anterior portion, and, internally, 

 the ventral muscle-scars are proportionately less than half as 

 large as in D. suhcarinata. 



Occurrence: Rockhouse shale at Rockhouse and the sulphur 

 spring, both on Horse Creek, Hardin County. 



FAMILY EICHWALDIID^ 



Dictyonella subgibbosa, n. sp. 



Plate H, figs. 11-13 



Description: Shell of medium to large size, subtriangular in 

 outline. Ventral valve strongly convex in the posterior half, its 

 beak prominent and large and strongly curved over that of the 

 dorsal valve. The sides of the beak form less than a right angle, 

 usually about 80°. The anterior part of this valve is occupied 

 by a broad shallow sinus slightly exceeding one third the width 

 of the shell. The sinus is generally distinctly marked at the 

 front of the valve, but it becomes shallower and indistinct posteri- 

 orly, continuing as a mesial flattening entirely to the denuded spot 

 on the beak. The dorsal valve is more gibbous and more nearly 

 oval in outline, its beak strongly incurved beneath that of the 

 opposite valve. At the anterior margin it bears a distinct but 

 broad low fold which becomes lower posteriorly and is lost in 

 the general convexity of the valve near its middle. The surface 

 reticulations are very fine and of nearly uniform size, over vari- 

 ous parts of the shell. The pits are about as long as wide, and 

 where well preserved appear nearly round or sometimes hex- 

 agonal. They are about one-half larger than those of D. gibbosa 

 and about one-half as large as the average of those in D. reticu- 

 lata. Counting along a row, twenty-eight to thirty of the pits 

 occupy a space of 5 mm. 



Discussion: Only fragmentary specimens of this species were 



