MAZATLAN BIVALVES 75 
Tablet 354 contains a minute valve, long. °05, and some frag- 
ments.—355, the most characteristic specimen. 
106. Venus (CHIONE) P UNDATELLA, Sow. 
Venus undatella, Proc. Zool. Soc. 1835, p. 22.—Hanl. Deser. 
Cat. p.117.—Sow. Thes. Conch. p. 711, pl. 153, f. 22. 
Chione undatella, Desh. B. M. Cat. Ven. p. 141, no. 68. 
Tablet 356 contains a broken very young shell which may 
belong to this species. Concentric ridges numerous; radiating 
costze just beginning to shew near margin: anterior tooth pro- 
longed, as usual in young shells. Long. ‘04. 
Hab.—On the shore, Isle Tres Marias, Gulf of California ; 
Col. Cuming.—? Mazatlan ; 1 valve, off Spondylus; L’pool Col. 
107. Venus (CHIONE) CoLUMBIENSIs, Sow, 
Venus Columbiensis, Proc. Zool. Soc. 1835, p. 21.—Hanl. 
Descr. Cat. p. 119: Wood Suppl. pl. 16, f.2.—Sow. Thes. 
Conch. p. 713, pl. 155, f. 53, 54.—B. WM. Cat. D’Orb. Moil. 
p. 68, no. 611. 
Chione Columbiensis, Desh. B. M. Cat. Ven. p. 136, no. 53. 
Shell remarkably solid, with strong ligament; with deep 
radiating grooves leaving broad flattened ridges which are 
crossed by fine concentric ridges, slightly elevated, rising and 
falling with the furrows, rather irregular, evanescent on the 
ventral portion, and nearly so on the posterior, where the ribs 
often rise into scales on the line of the ridges. The shells often 
show here and there concentric risings of growth, the fresh 
shell being commenced below the other. In one valve the 
posterior rib is very large, overlapping the other valve beyond 
the ligament. Lwunule defined by a deeply cut line, swollen in 
the middle, and bent at the margin. In these points, and in 
the character of the hinge, this species closely resembles Ch. 
verrucosa ; the pallial sinus however is somewhat larger. In 
more than half the specimens, the prevailing colour is choco- 
late brown; in the remainder, yellowish white more or less 
tinged with patches of purplish brown. The young shell is very 
often white, tipped at the umbos with pink or brownish purple. 
The smooth ligamental area is always spotted with purple. In 
the very young shells [?] the concentric ridges are not seen ; 
afterwards they often go nearly across. Colour inside, white, 
