152 CAKBONIFEROUS PERIOD. 



of the shell behind the ear would have a rhomboidal outline ; beaks mod- 

 erately prominent, separate ; liinge equal in length to about orfe-half the 

 full length of the shell, and its direction is nearly parallel with the posterior 

 half of the body ; posterior wing well developed, not sharply defined from 

 the body by an auricular furrow; its cardinal portion narrow and moderately 

 extended ; anterior ear obsolete ; lunule moderately large and deep, the 

 borders of which are slightly prominent laterally, but its margins sharply 

 rounded inward. 



Surface smooth in aspect, but it is marked by -very numerous fine lines 

 of growth. 



Length, from front to posterior extremity, about four centimeters ; 

 height, from base to hinge-margin, eighteen millimeters ; average width of 

 the body of the shell, about one centimeter. 



This shell somewhat resembles M. longisjpina (zr Gervillia longispina Cox) 

 from the Coal-Measure rocks of Kentucky; but it differs conspicuously from 

 that species in its more slender and less deeply-curved body, and in having 

 a shorter ear-spine than that species is represented to have by Professor 

 Cox's figure. 



Position and locality. — Strata of the Carbonifei'ous period; Camp Apache, 

 Maricopa County, Arizona. 



Genus MYALINA de Koninck, 1844. 

 Myalina (?). 



Associated with the foregoing at Camp Apache, some imperfect speci- 

 mens of Myalina were obtained, which appear to belong to M. recurvirostris 

 Meek and Worthen. 



Myalina ? Swallovi McChesney. 



Associated with the two foregoing species at Camp Apache, Arizona, a 

 few examples of Myalina f Swallovi were obtained, the best one of which is 

 represented by fig. 8 a, Plate XL 



