MAZATLAN UNIVALVES 375 
1766, 3 sp. spots shaded.—1767, 3 sp. spots few.—1768, 5 sp. 
very callous. 
Tablet 1769 contains 2 sp. with broad straight mantle mark.— 
1770, 5 sp. mantle mark irregularly waved.—1771, 3 sp. shew- 
ing changes in mouth. 
Abnormal specimens. Tablet 1772 contains 5 sp. after slight 
fractures.—1773, 5 sp. somewhat deformed by fracture.—1774, 
2 sp. twisted.—1775, 4 sp. after serious injury to labrum.—1776, 
4 do. labium.—1777, 1 sp. which has bridged over the aperture 
*22 in length, leaving a hole at the posterior canal.—1778, 3 sp. 
mantle irregularly injured.—1779, 4 sp. with large scar on the 
shoulder (not uncommon).—1780, 3 sp. with anterior scar, 
shewing violet layer.—These 120 specimens represent all the 
variations observed among many thousands. 
Genus TRIVIA, Gray. 
Zool. Journ. 1832, vol. i. p.1:— Proc. Zool. Soc. 1847, p. 142. 
Shell smail, front lirate, back with ribs or tubercles. 
Cyprea, pars, auct. 
439. Trivia pustuLATA, Lam. 
Cyprea pustulata, Lam. Ann. Mus. vol. xvi, p. 101, no. 56 :— 
An. s. Vert. vol. x. p. 535, no. 56.—Dillw. Deser. Cat. p. 469, 
no. 66.—Wood Ind. Test. pl. 17, f. 63.—Sow. Gen. f. 5:— 
Conch. Ill. pl. 102, f. 71.—Gray Zool. Journ. vol. i. p. 513.— 
Kien. Icon. Conch. p. 128, pl. 2, f. 3—Rve. Conch. Icon. 
pl. 15, f. 76.—Chénu Lec. Elem. pl. 2, f. 11, 12.—Mke. in 
Zeit. f. Mal. 1851, p. 33, no. 113.—C. B. Ad. Pan. Shells, 
no. 9, p. 35. 
Trivia pustulata, Gray Descr. Cat. p. 16, no. 138.—Pen. Cyel. 
vol. vill. p. 257. 
Pustularia pustulata, H. & A. Ad. Gen. i. 269. 
This extremely beautiful species when young has much the 
form of Simnia (Ovula) patula, with the spire entirely con- 
cealed, and the surface most delicately cancellated as in Ficula. 
On turning-in its labrum, it first develops white facial ribs on 
a dark ground, afterwards the pustules on the back, finally 
those terminating the ribs. There often appears a white layer 
at the sides, in which ease the lateral tubercles have generally 
a yellow tint; and always two ill-defined brown dashes, near 
