606 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



small, sharply raised, radiating lines are usually observable upon the 

 postero-dorsal portion of each valve. 



Length 67 millimeters ; height 39 millimeters. 



This species was described by me in vol. iv, part i, of Lieutenant 

 Wheeler's Explorations and Surveys West of the One Hundredth Meridian 

 (1876) as Unio vetustus Meek. A careful examination of fuller collec- 

 tions convinces me that they are specifically distinct. So far as I am 

 aware, Unio vetustus has been found only in the strata of the Laramie 

 group and in the vicinity of Old Bear Eiver City, Wyo. ; while U. 

 mendax is found in strata probably of the age of the Wahsatch group 

 at Wales, Utah, and also in the Caiion of Desolation of Green Eiver 

 in the same Territory. 



CEEIPHASIIDyE. 



Genus CASSIOPELLA (gen. nov.) 



Shell resembling Goniohasis in form, and in many of its other charac- 

 teristics, but, unlike that genus, this is distinctly umbilicated ; volu- 

 tions more or less convex or angular ; aperture more or less produced 

 in front, subovate or rhomboidal in outline ; outer lip sinuous ; inner 

 lip more or less callous upon the body-volution. 



This genus is proposed to include the species published by myself as 

 Leioplax f turricula in Powell's Eeport on the Geology of the Uinta 

 Mountains, page 133 (1876). I am by no means satisfied as to its true 

 family affinities, but place it jDrovisionally with Goniohasis, in the 

 family Ceripliasiidce of Gill. Being umbilicated, it bears nearly the same 

 relation to Goniohasis that Cassiope does to Turritella. 



Only one species referable to this genus has yet been recognized, but 

 among the typical specimens collected from the Wahsatch strata at Black 

 Buttes Station, Wyoming, is one the volutions of which are convex, and 

 not angular, like those of the typical examples; but a few distinct raised 

 revolving lines exist upon the anterior side of the last volution. This 

 specimen is distinctly umbilicated, and may possibly represent another 

 species of the genus here proposed, but I am at present inclined to 

 regard it as only a variet}^ of the typical species. 



