MAZATLAN BIVALVES 115 
and by the 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 greater part of the surface. Anterior adductor very near 
the margin. The outline varies considerably, but not so much 
as in the next species. 
The largest specimen measures long. 2°2, lat. 2°38, alt. 1°26. 
A transverse ,, ie Sey Ladies 2 Ons kenas edey Ota: 
An inflated vs S so) kO2 reels Si. haan 
Hab.—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 slightly produced, normal shape.—508, 2 do. margin 
regular, very transverse.—509, 2 do. less transverse.—510, 3 
do. very irregular outline.—511, 1 do. orbicular, aberrant, 
approaching aberrant forms of the next species. 
165. Cyrena Mexicana, Brod. and Sow. 
0.4. °C. olivacee” simulante, sed ventricosiori, forma maxime 
variante, suborbiculari, subtrigond, seu elliptica ; parte posticd. 
sew prolongatda, seu subcarinatd, seu rotundaté ; extus albescente, 
umbonibus plerumque maxtine erosis ; epidermide fusco-olivacea, 
lamellis creberrimis, non corrugatis, plerumque detritis ; 
intus alba, marginibus plus minusve violaced; dent. card. 
magis inequalibus, lat. magis extantibus ; sinu pallit minimo, 
marginibus paulum, divergentibus. 
Cyrena varians, P. P. C. Cat. prov. 
Pars=Cyrena Mexicana, Zool. Journ. vol. iv. p. 364.—Hanl. 
Descr. Cat: p.94.—B. M. Cat. Corbiculade, p. 260, no. 59. 
Var. =Cyrena altilis, Gould, Mex. § Cal. Shells, p. 27, pl. 16, f. 5. 
Jun.=Cyrena fragilis, Desh. ms. in Mus. Cuming. 
?=C. Floridana, Conr. Proc. Ac. N. 8S. Phil. iii. 1846, p. 23, 
pl. 1, f.1.—B. W. Cat. Corb. p: 257, no. 49. 
The original type of this species “in Mr. Sowerby’s collee- 
tion” appears to be lost, and the description is too meagre to 
separate it from its congeners: “OC. ¢. ellipticd, ventricosd, 
utrinque rotundata, antice breviore ; dentibus 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 
