MAZATLAN BIVALVES 107 
period of the Coralline Crag, it is natural to suppose that it has 
now a wide distribution, though its station is such as generally 
to elude discovery. It would be premature to pronounce 
absolutely on its specific relations, before the animals have 
been examined, and other seas more thoroughly searched. The 
extreme forms are quite sufficiently marked to allow of specific 
distinction, just as Capt. Brown has described 3 species from 
the British varieties ; but the known propensities of nestling 
bivalves, and the presence of intermediate specimens with ever 
varying characters, do not justify this course. The smallest 
specimen is ‘O02 across: the largest measures long. ‘24, lat. °26, 
alt. °15. 
Hab.—British seas, Auct.—Mediterranean, Philippi.—Cana- 
ries, MW’ Andrew.—Mazatlan ; not uncommon in crevices of 
shells, generally young; L’pool & Havre Coll[A species 
probably identical is from Peru; Col. Cuming.—The Chironia 
Laperousii of Desh., from Monterey, Mr. Hartweg, is quite 
distinct. |—Fossil: British Coralline Crag; Searles Wood. 
Tablet 485 contains 12 pairs, of various sizes.—486, 10 pairs 
of valves, very young.—487, 10 do, adolescent.—488, 2 sp. which 
had lived inside a dead Spheenia fragilis, which had lodged 
in the hole of a Lithophagus aristatus, which had bored in 
Murex regius.—489, 4sp. in situ, in Spondylus calcifer, Patella 
Mexicana, and Trivia sanguinea. 
Tablet 490 contains 1 sp. much inflated. 
Tablet 491 contains a pair of valves, with short truncated 
teeth : [P var. |—492, 2 pairs and a valve, orbicular. 
Tablet 493 contains 3 valves, ligamental pit prominent : 
[? var. ] 
Tablet 494 contains the valve with the honeycomb pattern. 
Genus LASEA, Leach. 
Lasea, Leach ms.—B. M. Cat. Br. Moll. pt. vii. p. 81 :— 
Phil. Hand. Conch. p. 345—Lasxa, Brown, Ill. Conch. Gr- 
Br. 1827.—Leszea, Moll. 1842 Phil. 1845. 
Bornia sp., Phi/. 1836. 
Cycladina, Cantraine, 1836, Bull. Ac. Se. Bruzx. 
Poronia, Récluz, 1843, Rev. Zool. p. 166. 
Kellia pars, Lorbes & Hanl. Br. Moll. 1850, vol. ii. p. 85. 
Autonoe, Leach, (a secunda manu,) Br. Moll. 289.2 
