54 COLORADO COLLEGE STUDIES. 



greatest dimension diverging from the liinge-line much more 

 widely than in the latter species; alar outline rounded; an- 

 terior margin descending steeply in a nearly straight line for 

 a considerable distance in front of the beaks, then curving 

 rather suddenly away toward the somewhat prominently con- 

 vex distal part of the basal outline, anterior and posterior 

 margins making nearly a right angle with each other: beaks 

 placed opposite the anterior extremity of the hinge, moder- 

 ately inflated, and moderately elevated above the hinge-line, 

 anteriorly flattened, but not abruptly so; hinge-plate rather 

 short, broad, the ligamental grooves crowded, more numerous 

 and longer than in /. labiatus, though ample and shallow; 

 valves thin, ornamented with numerous concentric rib-like 

 folds, which, on the discal and ventral parts, are quite strongly 

 elevated and much narrower than the intervals between them. 



Measurements. — Height 82, length 95, breadth 54, axis of 

 greatest dimension 107 mm. In some examples, the species 

 attains considerably larger dimensions. 



Occurrence. — This is the common Inoceramus of the 

 Duck creek (lower Washita) limestone, or basal part of the 

 Washita division of the Comanche series. The types were 

 collected by Mr. J. T. Munson and the writer one to two miles 

 northeast of Denison. Texas. The species occurs also in the 

 Chickasaw nation, three miles north-northwest of Marietta, 

 in the same limestone. At both localities it is associated 

 with Pcichydiscus marcidnus* Schloenhcichia peruvianci and 

 S. serrtaescens, Hamites fremonti, Epiaster elegans, var. 

 prcenunfius, etc. 



In the upper part of the Kiowa shales of southern Kansas, 

 occur imperfect casts of an Inoceramus which I provisionally 

 refer to this species. In Clark county, Kansas, these are 

 associated with Ostrea quadruplicata and Osfrea frcinkUni. 



*Ammonites IPachydiscus^ brazoensis, Shum. (1860), is a synonym of A. [P.] 

 marciana, Shum. (1854) ; but I am somowliat doubtful about the propriety of using 

 tlic older name, as the description and fiyuro accompanying it are those of a very 

 young specimen. It seems a strangi' circumstance that Dr. bhumard failed to 

 refer to the two names as synonymous. Tliis circumstance, however, may indicate 

 either that he did not recognize in '' brazoensia'''' his '"marciana" of 18.54, or that he 

 merely considered the older name invalid, as based on a young specimen and one 

 that did not show the suture. 



