160 CARBONIFEROUS PERIOD. 



behind to the left of the apex, remainder of the border having several 

 other more or less indistinct sinuosities, with all of which the lines of growth 

 upon the surface of the shell correspond. 



All the specimens in the collections, and also those in my private 

 collection, obtained from the same Upper Coal-Measure strata in Nebraska 

 that supplied Mr. Meek with the types of the species, have the apex a little 

 more curved than his type-specimen had, as may be seen by comparing the 

 figm-es on Plate XII with his illustrations (loc. cit). In other respects, our 

 examples correspond with his figures and descrij)tion, and I have little or 

 no doubt of their specific identity with P. Nehrascensis. 



Length, nineteen millimeters ; breadth, nine millimeters. 



Position and locality. — Strata of the Carboniferous period ; near Santa 

 F6, New Mexico. 



Family MAOEOOHEILIDJ]. 



Genus MACROCHEILUS Phillips, 1841. 



Macrocheilus anguliferus White. 



Plate XII, fig. 3 a, 6, c, d, e, and /. 



Macrocheilus anguliferus White, 1874, Expl. & Surv. west 100th Merid., Prelim. Rep. 

 Invert. Foss., 22. 



Shell of medium size, irregularly rhombic in outline by side-view ; 

 spire about equal in length to two-fifths the full axial length of the shell, 

 acutely pointed ; volutions six or seven, increasing somewhat raioidly in 

 size ; outer side of the volutions more or less convex, but the portion toward 

 the apex is usually a little flattened; posterior side narrow, usually squarely 

 ti'uncated, so as to form a distinct angle with the outer side. This angle is 

 usually more or less prominent, but in some cases it is nearly obsolete, in 

 which latter case the slight flattening of the posterior side merely produces 

 the appearance of a deeply-impressed sutui-e ; in the former case, there is a 

 distinct, gradually-diminishing spiral shelf extending from the hinder part 

 of the aperture to the apex ; aperture irregularly ovate, more or less truncated 

 behind by the shelf refei'red to, effuse below; outer lip sharp; columella a 

 little tortuous or nearly on a line with the axis of the shell. Sm'face apj^ar- 

 ently unmarked, except by the usual lines of growth. 



