MAZATLAN BIVALVES 115 



and by tlie rich olive epidermis, covering the umbos, and rising 

 into irregularly corrugated folds, which are very close on the 

 posterior part. The interior displays a very dark purple over 

 the gi-eater part of the surface. Anterior adductor verj^ near 

 the margin. The outline varies considerably, but not so much 

 as in the next species. 



The largest specimen measures long. 2*2, lai. 2"38, alt. 1*26. 



A transverse „ „ „ 1-7, „ 2-05, „ 1-06. 



An inflated „ „ „ 1'62, „ I'S, „ 1-16. 

 Sab. — Mazatlan ; not common ; L'pool Col. 



Tablet 505 contains 3 specimens much produced ventrally, 

 slightly so posteriorly.— 506, 3 do. less produced.— 507, 3 do. 

 very shghtly produced, normal shape. — 508, 2 do. margin 

 regular, very transverse. — 509, 2 do. less transverse. — 510, 3 

 do. verj' irregular outline.— 511, 1 do. orbicidar, aberrant, 

 approaching aberrant forms of the next species. 



165. Cyeena Mexicaka, Brod. and Sow. 



C. t. " C olJvacea;" simulante, sed ventricosiori, forma maxime 

 varlante, suhorbiculan, .•iuhtrigond, seu eUipticd ; parte posticd 

 seu prolongatd, seu suhcarinata, seic rotundatd ; extus alhescente, 

 umbonihics plerumqiie maxime erosis ; epidermidefusco-olivaced, 

 lamellis creherrhnis, non co 7' rug at is, 2}lerumque detritis ; 

 intus albd, marginibus plus minusve violaced ; dent. card, 

 magis incequalibus, lat. magis extantibus ; sinu pallii minima, 

 marginibus pauhim divergentibus. 



Cyrena varians, P. P. C. Cat. prov. 



Pars = CjTena Mexicana, Zool. Journ. vol. iv. p. 364. — Hani. 



Descr. Cat. p. 9k— B. M. Cat. Corbiculadce, p. 260, no. 59. 

 Var. = Cyrena altilis, Gould, Mex. SfCal. Shells, p. 27, pi. 16, f. 5. 

 Jun. = Cyrena fi-agilis. Desk. ms. in Mus. Cuming. 

 ■r' = C. Floridana, Conr. Proc. Ac. N. S.Phil, iii. 1816, p. 23, 



pi. 1, f. 1.—^. M. Cat. Corb. p. 257, no. 49. 



The original tj^pe of this species "in Mr. Sowerby's collec- 

 tion" appears to be lost, and the description is too meagre to 

 separate it from its congeners : " C. t. ellipticd, ventricosd, 

 utrinque rotundatd, antice breviore ; dentibns parvis, obtusis." 

 Nevertheless, as it is further stated to be "outside white, with 

 an olivaceous epidermis ; inside whitish, varied with reddish 

 violet ;" and as it came from Mazatlan, it is fair to conclude 



