70 MAZATLAN BIVALVES 
Genus CYTHEREA, Lam.* 
Cytherea, ex parte, Lam. 1809, et auct. 
Meretrix, Lam. 1799; Desh. B. M. Cat. Ven. p. 34. 
This genus, as restricted, is known by the subtrigonal form, 
crenated posterior and distant anterior tooth, and the very 
small pallial sinus. 
100. CYTHEREA PETECHIALis, Lam. 
Lam. An.s. Vert. ed. Desh. vol. vi. p. 299.—Sow. Gen. f. 1.— 
Hanl. Descr. Cat. p. 96 :—Wood Suppl. pl. 15, f. 9.—Rve. 
Conch. Syst. vol. i. pl. 69, 70, f. 1.—? Sow. Thes. Conch. p. 619, 
pl 129, £51. 
Meretrix petichialis, Hnac. Méth. pl. 268, f. 5, 6.—Desh. B. M. 
Cat. Ven. p. 36, no. 4. 
The widely extended form to which this shell belongs was 
distributed by Lam. under the species lusoria, petichialis, im- 
pudica, castanea, zonaria var. 1, meretrix and graphica.—Desh. 
in his edition of Lamarck regarded the 6 last, and C. lusoria 
probably, as all varieties of one species, differing only in colour, 
and displaying insensible gradations even in this. In the 
B. M. Cat. Ven. however he publishes them all as distinct (ex- 
cept meretrix which is merged into M. impudica), along with 
C. fusea, Koch in Phil. Abbild. Conch. p. 19, pl. 3, f. 1.—Sow. 
unites C. graphica with C. petichialis, C. fusca with C. lusoria, 
C. castanea with C. impudica, adding C. formosa on his own 
authority, and yet “‘being almost persuaded that” all these, 
along with C. meretrix, morphina, zonaria, casta and ovum 
Hani., “might be united under one name, seeing that they 
pass imperceptibly into each other, and that in a young state 
it is almost impossible to distinguish them.” If the varieties 
would arrange themselves into zoological provinces, there 
would be more hope of finding specific types ; but Iam unable 
to find any difference between the Mazatlan shells and those 
from the China and Japan seas. I found scarcely a dozen 
specimens in the D. chionea box of the Liverpool collection ; 
but several more were seen mixed with the other Mazatlan 
shells in the shop of a dealer who had surreptitiously obtained 
* The familiar Lamarckian name (‘‘nom plus convenable,’’ Lam.) is retained, 
because a man ought to be allowed to alter his own work if he can improve it ; 
as he certainly did in this instance, by rejecting a meretricious name for so beau- 
tiful a group of shells, There is nothing unchaste in nature: it is only man’s 
corrupt ideas that see unclean images in the purity of God’s works. 
