()l) COLORADO COLLEGE STUDIES. 



Measiirenicnfs. — Height (to summit of beaks) 92, vertical 

 dimension from base to hinge-line 7(), length 120, breadth 

 80 mm. 



Occurrence. — With Cyphosoma I'olanum, Enallastcr in- 

 Jlafus, Osh'ca rocuiokensis, Exogyrd. arietina, E. drakei, 

 numerous huge Vola texana, Roudairia denisonensis, and 

 many other fossils, in the Grayson marl in the abandoned 

 D. B. and N. O. railway cut about half a mile southeast of 

 the Union depot of Denison, Texas; also in the Choctaw 

 limestone, with Ostred <in(idrHpliccita, Exogyra arietina, 

 Terehrcdella ivacoensis.Pholadomya ragsdalei, etc., on sum- 

 mit of Pawpaw creek bluif southeast and east of Denison. 

 The species is apparently more common in the limestone 

 than in the marl, but the specimens thus far observed from 

 the former are usually smaller and more poorly preserved 

 than those from the latter. 



TeLLINA SUBiEQUALIS, Sp. TIOV. 



Shell subsequilateral, elongate-elliptical, the height con- 

 tained twice in the length, the outline a little narrowed toward 

 either extremity, slightly more toward the posterior than 

 toward the anterior, the dorsal outline gently declivous and 

 nearly straight for some distance on either side of the beaks, 

 the anterior outline evenly rounded, angulation of the pos- 

 terior slope scarcely appreciable in the cast, valves of moder- 

 ate convexity, the curvataire across the discs being remarkably 

 uniform from a little below the umbonal summits to the 

 basal margin and from the anterior to the posterior extremity; 

 beaks low and obtuse; pallial sinus extending forward a little 

 beyond the i^oint directly opposite the beaks, its fundus 

 rounded. 



Measurements. — Height of cast 14.5, length from anterior 

 extremity to a point opposite the beaks 18.5, from posterior 

 extremity to the same point (about) 15.5, convexity of cast of 

 right valve about 3 mm. 



Occurrence. — On Pawpaw creek, east of Denison, Texas, 

 in ochraceous shell-conglomerate of the Pawpaw clays; with 

 Yoldia inicrodonia, Turritella seriatim-granulata, etc. Oc- 

 curs chiefly as casts with fragments of shell, and as molds. 



