Length of the body in proportion with the width variable ; in some 

 specimens (perhaps broken ones) the length and width being about 

 equal, while in others the length is two or three times as great as the 

 width. The width, in different specimens, varies from three and a 

 half to upward of four centimeters. 



Position and locality. Same as the last. 



BEACHIOPODA. 

 Genus ACROTRETA Kutorga. 



ACROTRETA? SUBSIDUA (sp. nov.} Shell thin, corneous, discoid, sub- 

 circular or slightly suboval in outline, the transverse diameter being a 

 trifle greater than the longitudinal ; sides regularly and front broadly 

 rounded ; posterior margin slightly straightened, forming a compara- 

 tively short, slightly convex, or nearly straight hinge-line. Dorsal valve 

 nearly flat; beak marginal, not prominent. Interior with a slightly-raised 

 median ridge, beginning beneath the beak, and extending to about the 

 middle of the valve, where it disappears; impressions of the posterior 

 adductor muscles small and placed nearly beneath the beak, one on each 

 side of the median ridge ; between these muscular impressions and the 

 posterior margin there is, at each side, an obscure diverging ridge or 

 fold. 



Yentral valve moderately convex in the umbonal region, but more 

 flattened anteriorly ; apex excentric, somewhat prominent and minutely 

 perforate; adductor impressions small and placed in the apex close to 

 the foramen, one at each side of it. One of the specimens shows a slight 

 flattening of the triangular space between the apex and the hinge-line, 

 which appears like an indistinctly-defined cardinal area. 



This shell differs so widely in shape from the typical forms of Acro- 

 treta, although it seems to possess its other essential characteristics, 

 that I have referred it only provisionally to that genus. 



Length of the largest specimen, six millimeters ; width, seven mil- 

 limeters. 



Position and locality. Strata probably of the epoch of the Potsdam 

 Sandstone, Antelope Spring, House range, Utah. 



Genus TREMATIS Sharpe. 



TREMATIS PANNULUS (sp. nov.} Shell small, subcircular ; ventral valve 

 moderately convex ; apex prominent, excentric ; surface marked by a 

 very fine net-work of oblique, raised lines, dividing ib up into minute 

 four-sided pore-like pits, which cause it to resemble, under a lens, finely- 

 woven cloth. 



Diameter of the valve, about three millimeters. 



Position and locality. Shales of the Potsdam epoch, Pioche, Nevada 



PTEROPODA. 

 Genus HYOLITHES Eichwald. 



HYOLITHES PRIMORDIALIS Hall ? The collection contains specimens 

 of a Hyolithes from the shales of the Potsdam epoch at Pioche, Nev., that 

 seem to differ too little from H. primordialis Hall, from the strata of the 

 same epoch in Wisconsin, to warrant a full specific separation from it. 



