204. MAZATLAN UNIVALVES 
growth in the lower part; towards the apex stained with 
chesnut in the dark shells. The colour of the interior varies 
from pure snow white to very dark brown; generally more or 
less spotted or rayed with chesnut. The finest specimens 
were eagerly caught up by collectors: the largest I could 
find measures long. 1°72, lat.1°5, alé.-98. 
A flat sp. ct laa as a AOee Fea bs Peay fc 
Hab.—(C. tenuis) Samanco Bay, Peru; on living shells, in mud- 
dy sand, 9 fm.; Cuming.—(C. hispida) Isl. Muerte; on dead 
shells, in sandy mud, 12 fm.; Cwming.— C. maculata) Do. 
11 fm. Cwming.—Panama; under stones at low water mark, 
rare; C. B. Adams.—San Diego, Lieut. Green.—Monterey : 
very rare ; Nuttall.—Mazatlan ; not uncommon ; L’ pool Col. 
Tablet 1445 contains 3 sp. extremely young.—1446, 3 do. a 
stage older.—1447, 4 do. adolescent: on one a young Crepidula 
aculeata has fastened itself, wearing away the spines.—1448, 
1 sp. adult, with attachment of another. 
Specimens shewing form. ‘Tablet 1449 contains a series of 9 
sp. from very flat to conical.—1450, 3 sp. shewing crenations of 
the margin.—1451, 4 do. margin very irregular.—1452, 4 sp. 
curiously deformed and thickened by disease. 
Specimens shewing changes of surface. Tablet 1453 contains 
3 sp. nearly smooth—1454, 4 do. tubercular spines develop- 
ing.—1455, 4 do. spines regular and crowded.—1456, 6 sp. some 
spines greatly developed. 
Specimens shewing colour. Tablet 1457 contains 4 sp. white, 
developing chesnut rays.—1458, 5 do. light brown, scarcely or 
generally diffused.—1459, 4 do. tortoiseshell pattern.—1460, 4 
do. tortoiseshell changing into dark brown. 
Genus CALYPTRAAA, Lam. 
Calyptreea auct. (pars.) Subgen. Calyptrea, 6. Less. Brod. 
Calyptra, Humph. 1797, (pars). Gray, Proc. Zool. Soc. 1847, 
p. 157, no. 271.—H. & A. Ad. Gen. 1. 364. 
Mitrularia, Schum. 1817, Ess. no. 9.— Phil. Handb. Conch. 
p. 186. 
Lithedaphus, Owen, Proc. Zool. Soc. 1842, p. 147.—Litholepas, 
Gray, loc. cit. 
Cemoria, Misso, 1826; non Leach, nee Swans. 
