202 MAZATLAN UNIVALVES 
distinct radiating black lines. Sometimes the internal surface 
is beautifully mottled with purple or brown. The animal 
mark is by no means constant in shape ; but, when well defined, 
shews the body gathered pretty regularly into points with 
curves between. The smallest specimen is about *25 in length ; 
the largest measures long. 2°15, lat. 1°7, alt. °72 
Hab.—Mazatlan, Lieut. Shipley —S. W. Mexico, P. P. C.— 
Mazatlan very common; L’pool & Havre Coll. 
Tablet 923 contains 4 sp. various ages.—924, 4 specimens 
white.—925, 5 do. greenish tinge.—926, 4 do. coloured within.— 
927, 4 do. tortoiseshell.—928, 8 sp. yellowish tinge.—929, 4 do. 
very faint appearance of marginal dots.—930, 7 do. a shade 
more developed.—931, 8 sp. black rays coated over.—932, 7 sp. 
black dots distinct.—933, 7 do. more distinct.—934, 7 do. well 
developed.—935, 5 sp. faint black dotted margin.—936, 5 do. 
distinet black margin.—937, 6 sp. with brown tortoiseshell 
markings.—938, 5 do. purplish tinge.—939, 4 do. black and 
brown.—940, 3 sp. body mark distinct.—941, 3 sp. margin 
abnormally indented.—942, 5 sp. irregular internal growth.— 
943, 1 do. with large Balanus, Lithophagus, &e. 
Genus NACELLA, Schum. 
Patella, pars, auct. 
262. NacrenLta, ————., sp. ind. 
Tablet 944 contains a solitary specimen of a Nacella, of the 
shape and size of Ancylus fluviatilis, with the apex spirally 
recurved, and of a dark horny colour. It is not perfect enough 
for description. 
Hab.—Mazatlan ; off Chama, 1 sp.; L’pool Col. 
Famity ACM AID. 
Genus ACMA, Esch. ; 
Esehscholtz Zool. Ail. ed. Rathke, 1833, p. 16, (diagnosi copiosa.) 
—Forbes & Hanl. Br. Moll. vol. u. p. 434.—Woodw. Man. 
Moll. p. 155 —Phil. Handb. Conch. p. 199. (Non Acme, 
Hartm. 1821.) 
Lottia, Gray in Phil. Trans. 1833, and in Sow. Gen. 1833. 
Patelloida, Quoy & Gaim. 1834, Voy. Astr. vol. 11. p. 349. 
Tectura, Audouin § Milne Edw. Ann. Sc. Nat. 1830, vol. xxi. 
p. 226, (Gray: p. 325, Phil —H. & A. Ad. Gen. vol.i. p. 458. 
