52 COLORADO COLLEGE STUDIES. 



making an obtuse angle, its posterior margin rather more 

 than one and a half times as long as its dorsal. Left valve 

 unknown. 



Measiiremenis. — Height 9.5, length 8.75, convexity of left 

 valve 1 mm. 



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

 Texas, in red ochraceous shell -conglomerate of the Pawpaw 

 clays. The associate fossils are Ostrea quadruplicata, T(ipes 

 (lentonensis, YohUa niicrodonfa, Titrritella seriafiui-graiiii- 

 lata, S^jltenodiscus, Turrilites. etc. 



VOLA FREDERICKSBURGENSIS, Sp. UOV. 



This name is proposed for the species of Vola described 

 by Roemer from Fredericksburg, Texas, in \\\sKreidehildungen 

 von Texas, as " Peoten quadricostatus, var.," and is based on 

 his description and illustrations (pp. 64, (55; PL YIII, fig. 4 

 a, b,c). 



The species is the ordinary one of the Fredericksburg 

 division of the Comanche Cretaceous series, being very com- 

 mon in the Comanche Peak limestone of Texas and Indian 

 Territory, and in the lower parts of the Kiowa shales of 

 Kansas. 



It is easily distinguished from V. texanus, Roemer, by its 

 much narrower and more elevated ribs, more triangular form, 

 and usually (in adult examples) by its larger size. 



It has been referred to by authors under various names; 

 but it is distinct from any of the species to which it has 

 hitherto been referred. It is, however, closely allied to 

 V. alpina, D'Orb. 



AVICULA DISPAR, sp. nov. 



Shell small, semicircular, radiately ribbed, compressed, 

 very inequivalve, the left valve being feebly arched, its con- 

 vexity greatest in the basal region and its basal margin more 

 or less overhanging that of the smaller flat-concave right 

 valve; anterior ears sharply delimited, nearly equilateral tri- 

 angles; posterior ear feebly developed, narrow, rounded off 

 above on the distal part, that of the left valve not abruptly 

 separated from the body of the valve, that of the right valve 



