MAZATLAN UNIVALVES 289 



top. In this respect it differs from C. umbella, Desk. (Lam. 

 An. s. Vert. vol. vii. p. 635, no. 30, = C. rudis, Srod. Proc. Zool. 

 Soc. 1834, p. 35,) and the W. Indian form C. auriculata, Ckemn. 

 Conch. Cab. vol. x. f. 1628-9 ; of which, though common in 

 S. W. Mexico (P. P. CJ, 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 Calyptrsea 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 excavation. 



Aflat, spreading sp. measures long. 2*1, lot. 1*8, alt. '65. 



A conical one ,, 1'28, 1*15, '72. 



Hal). Lower California, Major Rick. Bay of Magdalena, 

 Gulf of California, Kellett^. W. Mexico, P. P. . Ac- 

 apulco, Col. Jewett. Panama, very rare, C. B. Adams. 

 Mazatlan ; not uncommon, on stones, dead shells, and 

 each other ; Upool Col. Straits of Magellan ; [?] Mr. 

 J. Robertson, B. M. 



Tablet 1432 contains a group of the fry, presented by E. 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, 1 sp. on Ostrea Virginica. 

 1442, a stone with thin shelly attachment.' 1443, Uvanilla 

 olivacea, with attachment of a Calyptrseid. 1444, A fragment 

 of, primitive rock, with 5 sp. in situ : (presented by J. Hib- 

 bert, Esq.) 

 Aug. 1856. bb 



