190 PALEONTOLOGY OF CALIFOENIA. 



C. COMPACTA, 11. S. 

 PI. 30, Pig. 85. 



Shell small, elongate subtrigonal, thick; beaks about a third 

 of the length from the anterior end ; cardinal margin sloping with 

 a slight convexity to the posterior end, which is narrowly trun- 

 cated; anterior end sloping, nearly straight above, broadly convex 

 and prominent below ; base nearly straight posteriorly, rounding 

 upwards regularly in advance, and most prominent under the 

 beaks; the lunule is almost entirely hidden in the matrix, but 

 appears to be large and deeply impressed. Surface polished and 

 marked by lines of growth in the middle, which develop into 

 small ribs anteriorly; an angular ridge runs from the beaks to 

 the posterior basal angle. 



Length, .95 inch; width, .68 inch ; height of single valve, .2 inch. 



A single valve, from the Martinez Group, Martinez, given me by Mr. Mathewson. 



This shell might be mistaken for the young of C. grandis, but it differs in being 

 more elongate posteriorly, in the possession of the marked angular ridge, in the 

 square posterior truncation, and in its greater convexity. 



UNIO, Retz., Auct. 

 U. Hubbardu, n. s. 



PI. 30, Fig. 86. 



Shell moderately large, thick, obliquely subquadrate; beaks 

 anterior, about a fourth of the length from the anterior end, 

 somewhat prominent ; posterior cardinal border straight (?) and 

 slightly sloping (from lines of growth on the younger portions of 

 the shell); anterior end regularly rounded and somtwhat prom- 

 inent; posterior end obliquely truncated; base nearly straight and 

 sloping behind, most prominent under the beaks, and curving 

 upwards regularly in advance; a strong angular ridge runs ob- 

 liquely downwards and backwards from the beaks to the posterior 

 basal angle. Surface marked by coarse, irregular lines of growth. 



