WHITE ON NEW INVERTEBRATES. 711 



surface-feature of the shell, but in some examples they are more or less 

 obsolete. Their character is similar to that of the markings upon U. 

 senectus and U. jjrimceous White, especially the latter. 



Length of the largest discovered example 82 millimeters ; height at 

 mid-length 48 millimeters ; thickness about 32 millimeters. 



The specific name is given in honor of Mr. Charles Aldrich, formerly 

 a member of the Survey. 



Position and locality. — Upper part of the Laramie Group, Black Buttes 

 Station, Union Pacific Eailroad, Wyoming, where it is found associated 

 with TJ. braehyopistJms, U. couesi, V. endliclii, U. propheticus, U. primw- 

 vus, TJ. kolmesianus, TJ. goniamhonatus White, and apparently with one 

 or two other species of this genus. 



Genus CORBICULA Mergele. 



CorMcula clehurni (sp. nov.). 



Shell large, subtrihedral in marginal outline ', height from base to umbo 

 equal to the extreme transverse length, moderately gibbous and its sides 

 regularly convex, flattened or a little concave along the postero-dorsal 

 portion, concave in front, where there is an almost defined lunule ; test 

 thick, or even somewhat massive in the case of old shells ; dorsal line 

 forming a somewhat regular convex curve from the beak to the postero- 

 basal portion, which latter portion is abruptly, sometimes almost angu- 

 larly, rounded to the base; basal margin almost regularly rounded up to 

 the antero-cardinal margin, but its convexity is usually a little greatest 

 in front of the mid-length ; antero-cardinal margin straight or slightly 

 concave, meeting the autero-basal margin at an obtuse angle or a promi- 

 nent abrupt curve ; beaks prominent, elevated, curving inward and for- 

 ward, and ending in a well-defined point when well preserved, as most 

 of the examples are; lateral teeth strong, well developed, and finely 

 creuulate ; cardinal teeth well developed, the outer posterior one in one 

 example showing faint crenulations, but otherwise of the ordinary char- 

 acter; pallial line distinct, somewhat distant from the margin; sinus 

 small, directed strongly upward. Surface marked only by the usual 

 lines and undulations of growth. 



Height of the largest example 42 millimeters; extreme transverse 

 length about the same; thickness 32 millimeters. 



This species bears more resemblance to C. cytheriformis M. & H. than 

 to any other published species; but it may be distinguished from that 

 species by its more distinctly trihedral outline, its greater proportionate 

 height, and its concave, almost lunulate front. 



Position and locality. — Laramie Group, Crow Creek. Colorado, about 

 12 miles north of its confluence with South Platte River. 



CorMcula cardiniceformis (sp. nov.). 



Shell somewhat above medium size for a species of this genus, trans- 

 versely subelliptical, moderately gibbous, especially a little forward of 



