CYRENA. ]5 



Cyrenn trlangxda, v. d. Bnscu, Philip, Abbild. Ill, 1S49, 78, pi. 2, f. 3, 

 Cijrena altllis, Gould, Bost. II. VI, 1852, 400, pi. xvi, f. 5, bis. 

 Cyrena variarts, Carpenter (pars), Mazatlan Shells, 1857, 115. 

 Cyrena mexicana, Carpenter (pars), loc. sub. cit. 1857, 115, 



Under the description of C. mexicana will be found a state- 

 ment of my reasons for separating these two species, wliich have 

 been confounded by Mr. Carpenter. The G. aUilis, Gould, which 

 I consider identical with this species, differs a little from v. d. 

 Busch's original type of G. triangula as figured in Philipj)], 

 in being smaller, a little more swollen, and in having more promi- 

 nent and more acute beaks ; in the main, however, it is the same 

 shell. 



Compared with G. radiata it is less solid, larger, more tri- 

 angular, the surface is smoother and the cardinal teeth are more 

 delicate ; it differs from G. olivacea in being more triangular, less 

 elongated, more inflated, the epidermis is thinner and the cardinal 

 teeth are more delicate. 



Mr. Reigen seems to have found this species in abundance. 



6. Cyrena ol>sclira, Prime. — Shell subtrigonal, heart-shaped, in- 

 flated, solid, tumid, subequilateral ; anterior side rounded ; posterior 

 broader, rounded, subtruncated at extremity ; beaks large, prominent, 

 slightly eroded ; valves heavy, full, interior white with markings of violet 

 on the margins ; striae regular, deep ; epidermis blackish-brown ; hinge- 

 margin curved, moderately broad ; cardinal teeth unequal, divergent ; 

 lateral teeth elongated, narrow, anterior tooth nearer the cardinal teeth, 

 larger, acute. 



Long. 1.80; Lat. 1.70; Diam. 1.06 inches. 

 " 48 ; " 44 ; " 33 miU. 



Hah. Soutb America. (Cabinet of Cuming.) 



Cyrena obscura, Prime, Proc. Zool. XXVIII, 1860, 321, 



The only specimen I have seen of this species is the one in Mr. 

 Cuming's collection. Compared with G. insignis, it is much less 

 inflated and more equilateral ; it is fuller and transversely less 

 elongated than G. olivacea. 



T. Cyrena insignis, Deshates. — Shell ovate-cordiform, thick, 

 coarse, inequilateral ; anterior side somewhat the shorter, broadly rounded ; 

 posterior side broad, truncate, obtusely angular ; beaks large, tumid, some- 

 what oblique, opposite, eroded ; striae coarse, irregular more numerous on 



