MAZATLAN BIVALVES 75 



Tablet 354 contains a minute valve, long. '05, and some frag- 

 ments. 355, the most characteristic specimen. 



106. VENUS (CHIONE) ? UNDATELLA, Sow. 



Venus undatella, Proc. ZooL Soc. 1835, p. 22. Hani. Descr. 



Cat. p. 117. Sow. Thes. Conch, p. 711, pi. 153, f. 22. 

 Chione undatella, Desk. B. M. Cat. Yen. p. 141, no. 68. 



Tablet 356 contains a broken very young shell which may 

 belong to this species. Concentric ridges numerous ; radiating 

 costa3 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. PMazatlan; 1 valve, off Spondylus ; L'pool Col. 



JL 107. VENUS (CHIONE) COLUMBIENSIS, Sow. 



Venus Columbiensis, Proc. Zool. Soc. 1835, p. 21. Hani. 



Descr. Cat. p. 119 : Wood Suppl. pi. 16, f. 2. Sow. Thes. 



Conch, p. 713, pi. 155, f. 53, 54 B. M. Cat. D Orb. Moll. 



p. 68, no. 611. 

 Chione Columbiensis, Desk. 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. Lunule 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, 



