292 REPORT UNITED STATES GEOLOGICAL SURVEY. 



regularly convex ; sides a little flattened above tlie middle ; rostral por- 

 tion narrowed, elevated, arched ; beaks situated well toward the front, 

 much elevated above the hinge-line, prominent, incurved, api)roximate, 

 and turned very slightly, if any, forward ; hinge-margin moderately long 

 for a species of this genus ; front having a short, oblique truncation 

 above, from the lower end of which the whole free margin of the shell is 

 continuously rounded to the posterior extremity of the hinge, the con- 

 vexity varying, but not very greatly, in different parts. Surface marked 

 by very numerous fine costse of nearly uniform size on all parts of the 

 shell, every third one of which only, bears upon its back many small 

 nodes or short spines. 



Height, from base to beak, 35 millimeters ; width, 36 millimeters. The 

 height is, however, sometimes greater than the width. 



This species bears more resemblance to G. curtum Meek & Hayden 

 than to any other species of Gardium yet described fi?om the Cretaceous 

 rocks of the West, but the prominent umbonal ridge, and the coarser 

 and non-spiniferous costse of that species, besides many other details, 

 clearly separate it from the species here described 5 the peculiar charac- 

 ter of the surface-markings also separate it from any other described 

 species with which it is in any danger of being confounded. 



Position and locality. — Cretaceous strata, probably equivalent with the 

 lower portion of the Colorado Group; head of Waterpocket Caiion, 

 Southern Utah. Collected by Mr. G. K. Gilbert. 



Cardium 1 



Plate 9, figs. 2 a, i, and c. 



The illustrations of this species on plate 9 were drawn by Mr. Meek 

 only a short time before his death, and were irrtended to represent a new 

 species, which, however, I have not yet been able to identify by speci- 

 mens in the collections of either the Survey or Smithsonian Institu- 

 tion. Therefore no description is attempted, but the illustrations are 

 given for the purpose of presenting to the public the latest labors of 

 that distinguished author, and to aid in the future identification of the 

 species. The illustrations represent a species closely related to the 

 C. curtum of Meek and Hayden ; but it dilfers conspicuously from tliat 

 species in having the costse that cover the space behind the umbonal 

 ridge smaller (instead of larger as they are in that species) than they 

 are on the greater surface of the shell in front of the ridge. Upon its 

 identification by discovered specimens, I propose for it the name G. ulti- 

 mum, in allusion to the last work done by the late Mr. Meek. 



Trapezitjm trunoatum Meek. 



Plate X, figs. 6 a and 1). 



Pachymyaf truncaia Meek, 1871, An. Rep. U. S. Geol. Snrr. Terr, for 1870, p. 301. 

 Trapezium truncatum Meek, 1873, An. Rep. U. S. Geol. Surv. Terr, for 1872, p. 493. 



" Shell small, longitudinally oblong, very convex ; posterior side long, 

 distinctly and rectangularly truncated, apparently closed ; pallial mar- 

 gin nearly straight and slightly sinuous along its entire length ; anterior 

 margin truncated a little obliquely forward from the beaks to the rather 

 prominent and abruptly rounded, or subangularly anterior basal extrem- 

 ity ; cardinal margin nearly straight and parallel to the base ; beaks 

 depressed nearly to the horizon of the dorsal margin, very oblique, some- 

 what compressed, and placed less than one-fifth the length of the valves 



