MAZATLAN UNIVALVES 289 
top. In this respect it differs from C. umbella, Desh. (Lam. 
An. s. Vert. vol. vil. p. 635, no. 30,=C. rudis, Brod. Proc. Zool. 
Soc. 1834, p. 35,) and the W. Indian form C. auriculata, Chemn. 
Conch. Cab. vol. x. f. 1628-9; of which, though common in 
S. W. Mexico (P. P. C.), not a single specimen was found 
in the Mazatlan collection. ‘This latter species is generally 
longer, more spreading, of a lighter colour, and with the cup 
only adherent close to the vertex. The ribs are also less 
developed, and never pitted. The Calyptrea auricularis of 
Deshayes may be the young of either species. The Mazat- 
lan shell is generally of a rich metallic brown, displaying a 
lighter or {deeper tint, sometimes nearly black; rarely of a 
light grey or flesh colour; occasionally tinted with green. The 
cup is always white, with transparent lines of growth. Its 
inner margin is scarcely flattened, and not angulated as in C. 
spinosa. When the creature lives on hard pebbles, there is 
generally an extremely thin shelly deposit: when on shells, a 
well marked excavati®n. 
A flat, spreading sp. measures long. 2°1, lat. 1°8, alt. 65. 
A conical one ys 36 1 WEE 2Z8 lg OMe ee 
Hab.—Lower California, Major Rich.— Bay of Magdalena, 
Gulf of California, Kellett—S. W. Mexico, P. P. C.—Ac- 
apulco, Col. Jewett.—Panama, very rare, C. B. Adams.— 
Mazatlan ; not uncommon, on stones, dead shells, and 
each other; L’pool Col.—Straits of Magellan; [?] Mm. 
J. Robertson, B. M. 
Tablet 1432 contains a group of the fry, presented by R. D. 
Darbishire, Esq. . 
Tablet 1433 contains 7 sp. very young.—1434, 5 do. young.— 
1435, 4 do. adolescent.—1436, 8 sp. shewing gradations of col- 
our from very light to nearly black.—1437. 4 sp. varying from 
very much to scarcely pitted ; margin much or scarcely palma- 
ted.—1438, 4 do. varying from very conic to spreading; ribs 
few (20), with large palmations, or many (42), with very small 
ones.—1439, 1 sp. with a young one adhering. — 1440, 2 sp. 
worm-eaten, cup diseased.—1441, I sp. on Ostrea Virginica.— 
1442, a stone with thin shelly attachment.— 1443, Uvanilla 
olivacea, with attachment of a Calyptreid.—1444, A fragment 
of primitive rock, with 5 sp.in situ: (presented by J. Hib- 
bert, Esq.) 
Aug. 1856. bb 
