114 INVERTEBRATE PALEONTOLOGY. [WHITE. 



Surface marked by the usual lines of growth, and also by numerous 

 extravagant and irregular concentric folds or wrinkles. 



This species belongs to the section of the genus that Brongniart has 

 designated under the name of Catillus. It is a peculiarly well-marked species 

 and easily distinguished from all others found in the rocks of the great 

 Rocky Mountain region. 



Transverse length of an average-sized specimen seven and a half centi- 

 meters; height from base to hinge, five centimeters. Specific name given 

 in honor of its discoverer, Mr. G. K. Gilbert, geologist of one of the survey- 

 ing parties. 



Position and locality. Salt Wells Group; near Last Chance Creek, 

 Southern Utah. 



Inoceramus Howelli (sp. nov.). Shell of medium size, obliquely and 

 irregularly suboval in marginal outline, the vertical diameter being greater 

 than the transverse; both valves having considerable convexity, that of the 

 left valve greater than the other; beaks narrowed, prominent, the prominence 

 of the left one greater than the other, both of them elevated above the 

 hinge line, and also curving forward beyond the front of the shell; front 

 flattened, extending almost straight downward from the front end of the 

 hinge, with which it forms nearly a right, or slightly obtuse, ang-le. Antero- 

 basal margin abruptly rounded to. the base; basal margin short; postero- 

 basal margin extending obliquely upward to the posterior extremity, straight- 

 ened or slightly emarginate; posterior extremity abruptly rounded to meet 

 the almost straight postero-dorsal margin. 



Between the axis of the body of the shell and the postero-dorsal margin 

 there is upon each valve a rather broad, shallow, but more or les*s distinct 

 furrow or depression, extending from the umbonal region to the postero- 

 basal margin, and ending at the emargination before mentioned. There is 

 also a distinct alation upon each valve, separated from the body portion by 

 a tolerably well-defined auricular furrow. 



Surface marked by the ordinary lines of growth, and also by moder- 

 ately distinct concentric folds, but the surface has a rather smoother aspect 

 than is usual with species of this genus. Height of an average-sized example, 



