DESCRIPTIONS OF INVERTEBRATE FOSSILS. 58 



scarcely observable; beaks inconspicuous, the entire umbonal 

 retijion strongly compressed, the beak of the left valve higher 

 than that of the right; valves thin; ligament double, the 

 outer part placed in an open groove, the inner in a triangular 

 pit under the beaks; hinge-plate of left valve broader than 

 that of the right; radial ribs of left valve large, broad, flat- 

 convex, separated by narrow, abruptly impressed intervals, 

 the intermediate ribs in the type-specimen not extending 

 over the somewhat strongly convex basal region, which is 

 smooth or finely concentrically striate and pearlaceous, but 

 suddenly truncated; ribs of right valve feebly developed, 

 narrow, irregularly tuberculated, obsolete on the ventral and 

 anterior parts; radial groove separating anterior ear from 

 body of valve, in the left valve, deeply impressed, and having 

 its counterpart on the right valve in a low ridge. 



Measurotwnfs. — Height 20, length H3, breadth 5 mm. 



Occurrence. — The type of this species is a finely preserved 

 shell found by the writer in the Grayson marl, on a draw of 

 Pawpaw creek, half to three-quarters of a mile southeast of 

 the Union depot at Denison, Texas. It was associated with 

 Exogyra arietina, E. drakei, Turrilites brazosensis, etc., in 

 the lower part of the marl. 



The ribs of the body of the left valve are fourteen in 

 number, and adjacent to either ear is a radially striated seg- 

 ment about as wide as the widest rib. The anterior ear of 

 the left valve shows two or three rather coarse ribs on the 

 posterior part, the posterior ear being ornamented with radi- 

 ating raised lines. In the narrow intervals between several 

 of these lines and between several of the broad ribs of the 

 posterior part of the body of the left valve, the hand-lens 

 reveals more or less regularly arranged elements that present 

 the appearance of cross-threads or obliquely compressed 

 tubercles. 



I am not acquainted with any species that is closely anala- 

 gous to Avicula dispar. 



Inoceramus comancheana, sp. nov. 

 Shell equivalve, obliquely and broadly rhombic-ovate, 

 more gibbous than that of I. labiatus, Schloth., the axis of 



