22 



anterior ear, they are coarser than those of the body of the valve, aud 

 soiuevrbat corrugated. Eight valve uukuowu. 



The specimens are all broken in some parts, but the height, anterio- 

 posterior breadth, and length of the hinge-line all seem to be about 

 equal — about six centimeters in the largest example. 



This shell somewhat resembles A. occidental i s Shumard, but differs in 

 its greater proportionate width, in being- less contracted below the ears, 

 its less distinctly defined posterior ear, its finer and more unequal costai 

 and greater size. 



Position and locality. — Carboniferous strata, east of Mount Taylor, 

 one mile south of Pajuate, Xew Mexico. 



Genus Mo>'OPTERIA Meek and Worthen. 



Mo>'OPTERiA Maeiax (•■*;;. nor.) — Shell nearly or quite equivalve, 

 slender, much extended posteriorly, curved : curvature greatest in the 

 anterior half of the shell : posterior half nearly straight : body gradually 

 tapering- to near the posterior end, which is sharply rounded ; a more 

 or less prominent angle is sometimes, in part, raised as a distinct ca- 

 rina, which extends along the middle of the body of each valve from the 

 beak to the posterior end: from this carina or angle the sides slope 

 abruptly to the inferior aud upper borders, so that a section of the shell 

 behind the ear would give a rhomboid outline. Beaks moderately prom- 

 inent, separate : hinge equal in length to about half the full length of 

 the shell, and its direction nearly parallel with the posterior half of the 

 body : posterior wing well developed, not sharply defined from the body ; 

 cardinal portion moderately extended ; anterior ear obsolete ; luuule mod- 

 erately large and deep, its margins sharply rounded. 



Surface somewhat smooth in appearance, but is maiked by very numer- 

 ous tine lines of growth. 



Length from front to posterior extremity, four centimeters : height 

 from base to hinge-margin, eighteen millimeters ; average width of the 

 body of the shell, about one centimeter. 



This shell is related to M. longisi)ina Cox (sp.) but differs from that 

 species in its more slender aud less deeply-curved body, aud in having a 

 much shorter ear-spine than the one represented in the figure given by 

 Professor Cox. 



Position and locality. — Strata of the Carboniferous period, Camp 

 Apache, Arizona. 



GASTEEOPODA. 



Genus Macrochellis Phillips. 



Macrocheilus angultfera {sp. nov.) — Shell of medium size, irreg 

 ularly rho-mljic in outline by side-view ; spire about equal to two-fifths 

 the full height of the shell, acutely pointed ; volutions six or seven, 

 increasing somewhat rapidly in size, more or less convex : but in some 

 cases the upper part of their sides is considerably flattened, and the 

 upper portion of the volution squarely truncated to the suture, forming 

 a distinct angle with the side. In other cases, the angle is less distinct ; 

 but it is perceptible in all, and in all the suture is distinctly impressed. 

 When the angle is distinct, there is a well developed spiral shelf extend- 

 ing from the upper margin of the aperture to the apex. Aperture 

 irregularly oval, more or less truncated above by the shelf referred to, 

 effuse below; outer lip sharp: columella a little tortuous, or nearly on a 



