50 MAZATLAN BIVALVES 
Tablet 248 contains 3 young specimens, dull ash colour, 
slightly rayed, one with slight gape.—249, 1 sp. adolescent, 
closed, slightly rayed on one valve, the other mostly dull 
brown.—250, 1 sp. larger, closed, margin waved.—251, 1 fine 
adult sp. gaping posteriorly and ventrally.—252, 2 sp. very 
slightly gaping, rays clouded.—253, 1 do., form undulata, gap- 
ing nearly all round.—254, 2 do. form and colouring intermedi- 
ate; one gapes posteriorly, the other ventrally.—255, 2 pairs 
and 2 valves, form undulata, large posterior gape.—256, 3 do. 
valves closed; of which one is nearly white inside, another of 
a rich diffused violet. Similar differences of colour may be . 
observed in the other specimens. 
Genus DOSINIA, Scopoli. 
Dosinia, Scop. Intr. ad Hist. Nat. p. 399, (1777).— Desh. 
B. M. Cat. Ven. p. 5. 
Artemis, Poli, Test. utr. Sic. p. 98, t. 1. (1791). 
88. DosIntA PPONDEROSA, Gray. 
Artemis ponderosa, Gray Anal. (1838), vol. vii. p. 309.— Rve. 
Conch. Icon. pl. 1. f. 4.—Hanl. Descr. Cat. p. 109, pl. 19. 
f. 38.—Sow. Thes. Conch. p. 656, no. 3, pl. 140, f. 2. 
Dosinia ponderosa, Desh. B. M. Cai. Ven. p. 7, no. 5. 
Cytherea gigantea, Phil. Abbild. Conch. Cyth. p. 33, pl. 7, f. 1. 
DANO. 1 . 
Venus cycloides, B. WM. Cat. D’ Orb. Moll. p. 67, no. 596. 
A single specimen in beautiful condition, after being referred 
to D. econcentrica (Gulf of Mexico), and D. distans (unknown ; 
probably Puerto Portrero), was at last doubtfully affiliated to 
this species by Mr. Cuming. A larger specimen procured 
since from another dealer, and probably from the same collec- 
tion, confirms the judgment. It is remarkable for the very 
orbicular form, slightly angulated beyond the ligament ; deeply 
cut lunule; and very regular and distant sulei, not obsolete in 
the middle, of which, measuring from 1 to 1°5in. from the 
umbo, there are only 8. The epidermis is extremely glossy, of 
a very light straw colour. Long. 1°64, lat. 1°74, alt. °73. 
Hab—Gulf of California, in sandy mud at low water, Sowerby. 
—Peru; Payta, D’ Orbigny—Mazatlan ; extremely rare; 
LP’pool Coil. 
Tablet 257 contains the specimen. 
