42 CONIRIBDTIONS TO CANADIAN PALAEONTOLOGY. 



Surface nearly smooth but marked with very fine and closely 

 arranged concentric stria;, also by a few distant lines of growth, which 

 latter are waved and toothed on the ]_iosterior area, where they are 

 crossed by obscure, rounded, radiating ribs. These ribs, though 

 obsolete above, are sufiiciently well marked below to cause an inter- 

 locking of the margins of the valves at the posterior end of the base. 



Hinge dentition unknown ; anterior and posterior muscular scars 

 nearly ecjual in size, the anterior broadly subovatc and higber than 

 broad, the posterior somewhat pointed both above and below ; pallial 

 line not clearly indicated. 



Dimensions of an average individual : length, twenty-three milli- 

 metres ; maximum height, twenty-one mm. and a-half ; thickness 

 through the closed valves, seventeen mm. A large cast of the interior 

 of a shell, from near Eoss Coulee, which is probably referable to this 

 species, measures forty-one millimetres in length by thirty-nine in 

 height. 



St. Mary Eiver, near its junction with the Belly Eiver, G. M. Dawson, 

 1881, and T. 0. Weston, 1883 : very abundant. St. Mary Eiver, W. 

 of MacLeod Benton Trad, E. G-. McConnell, 1881, and South Saskatche- 

 wan, opposite Swift Current Creek, E. G. McConnell, 1882. Three 

 miles north of Eoss Coulee, near Irvine Station, on the Canadian 

 Pacific Eailway, T. C. Weston, 1884, associated with P. subquadrata. 



Callista (dosiniopsis) deweyi. Meek and Hayden. 



Plate ij, figs. 4, 5, and 5 a. 



CytJierea Dciceyi, Meek and Hayden. 1S56. Proc. Ac. Nat. Sc. Phil., vol. VIII., 



p. S3. 

 Mcnirix Deweyi, Meek and Hayden. 1860- lb., vol. XII., p. 185. 

 Callista Deweyi, Meek and Hayden. 1861. lb., vol. XIII., p. 143. 

 Callista (Dosiniopsis) Deweyi, Meek. 1876. Kep. U.S. Geol. Surv. Terr., vol. IX., p. 

 182, pi. 17, figs. 15a, b, c, d, e. 



Bull's Head, about twenty-two miles west of the west end of the 

 Cypress Hills, E. G. McConnell, 1883 : five specimens, some of which 

 shew the hinge dentition well, and others the pallial sinus. Hill 

 south of Big Plume Creek, Township 8, Eange 5," west of 4th Principal 

 Meridian, E. G. McConnell, 1883 : nine unusuallj- perfect examples of 

 a shell which is probably only a large form of C. Deweyi, but which, in 

 shape and size, approaches very closely to the C. Owenana of Meek and 

 Hayden. 



In the " Palaeontology of the Black Hills of Dakota" (page 416) 

 Prof. Whitfield places C. Deweyi among the synonyms of Morton's 



