MAZATLAN BIVALVES 77 
ventral margin. The colour is very light brown, more or less 
spotted or stained with darker in zigzag stripes or blotches. 
The ligamental area is smooth, and marked off by a decided 
keel on each side. The keel is almost always painted with spots, 
even when the rest of the shell is without them. ong. 1°34, 
lat. 1:58, alt. °8. 
Hab.—Real Llejos & St. Elena, in muddy sand at low water, 
Cuming.—Ecuador, St. Elena, D’ Orbigny.— Mazatlan; ex- 
tremely abundant ; L’pool & Havre Coll. 
Tablet 364 contains 7 specimens with dark patches of brown. — 
365, 7 do. smaller patches.—366, 7 do. very small patches.— 
367, 7 do. dark markings obsolete.—368, 7 do. with generaliy 
diffused shade of lighter brown.—369, 7 do. the same broken 
up into patches. 
110. Taps GRATA, Say. 
Sow. Thes. Conch. part 13, p. 699, pl. ch., f. 152: (non Desh. in 
B. M. Cat. Ven. p. 170.) 
Venus grata, Say Am. Conch. 1830, pl. 26 (teste Jay, 36 teste 
Sow.) 
Chione grata, Desh. in B. M. Cat. Ven. p. 140. 
=(teste Desh.) Venus tricolor, Sow. Proc. Zool. Soc. 1835, 
p. 41.—Zool. Beech. Voy. p. 151, pl. 41, f. 7—Hanl. Deser. 
Cat. p.119: Wood Suppl. pl. 16, f.32.—(Tapes t.) Sow. Thes. 
Conch. p. 699, pl. 151, f. 153. 
=(teste Jay) Venus discors, Sow. Proc. Zool. Soc. 1835, p. 42.— 
Hanl. Deser. Cat. p. 118: Wood Suppl. pl. 15, f. 60—B. M. 
Cat. D’ Orb. Moll. p. 67, no. 600.—C. B. Ad. Pan. Shells, 
p. 269, no. 436.—(Tapes d.) Sow. Thes. Conch. p. 698, pl. 151, 
f. 148-150.—(Chione d.) Desh. B. M. Cat. Ven. p. 141, no. 65. 
?= Venus Entobapta, Jonas Zeit. f. Mal. 1845, p. 66. 
?= Venus neglecta, Phil. Abbild. i. 62, pl. 4. f. 3, (non Gray.) 
‘ This shell differs from T. histrionica in not having the smooth 
ligamental area nor the enclosing carine. The lunule also is 
less distinct. The large specimen is much more tumid, and 
more irregularly marked. The hinge teeth are much closer 
and smaller in proportion, and are very slightly bifid.—Pallial 
sinus less angulated, smaller. Internal crenations less distinct. 
An intermediate specimen has one tooth in each valve strongly 
bifid, and is flattened like T. histrionica. The youngest speci- 
men scarcely displays bifidity, is much more coarsely and 
regularly marked, and has the pallial sinus rounder. It is 
