MAZATLAN UNIVALVES 479 
fixed rather slanting on the rest, and deciduous. The next are 
furrowed with about ten strong ridges, of which one makes an 
angular keel, decussated by five ridges of growth. Afterwards 
the keel becomes tuberculous, and numerous intercalary lines 
appear while the ridges become obsolete. The shell often 
develops two fainter rows of tubercles below the principal 
ones. The operculum differs from that of P. patula in being 
much lighter, of a reddish brown ; inside more coarsely corru- 
gated transversely, with the nucleus of the scar indented ; out- 
side with two wings faintly marked off by diagonal lines. The 
largest specimen found, (allowing for the decollated apex,) 
measures long. 3°7, long. spir. 1°25, lat. 2°5, div. 75°. 
A depressed sp. ,, 2°1, xh “BS; 4° L644 a 100Y 
An elevated sp. ,, 2°35, it "SD, eg LR Oe ee FOR 
Hab.—Acapuleo, Humboldt & Bonpland.— Monte Christi ; 
under stones at low water; Cuming.— Panama; common, 
under stones, near low water mark of neap tides; C. B. Ad- 
ams.—Mazatlan ; extremely abundant ; L’pool & Havre Coll. 
Tablet 2232 contains a small shell, *13 by ‘07, probably 
belonging to this species. It consists of 5 whirls, of which the 
four first are nuclear and nearly smooth; the fifth is strongly 
costate, with 9 rounded ribs, of which two appear larger than 
the rest, and are crossed by fine layers of growth. Colour 
ashy, spotted with purplish brown. 
Tablet 2233 contains 6 sp. depressed variety.—2234, 6 do. 
more elevated.—2235, 4 do. fainter knobs.—2236, 5 sp. elevated, 
uniform tint.—2237, 4 do. faint knobs.—2238, 5 sp. do. paint- 
ed.—2239, 3 do. strong knobs.—2240, 7 sp. strongly lirate.— 
2241, 7 sp. shewing varieties of markings.—2242, 2 sp. uniform 
reddish brown.—2243, 3 sp. mended after fracture. 
Tablet 2244 contains the only very young sp. certainly 
identified.—2245, 6 normal opercula. Many will also be found 
with the shells.—2246, 1 very large do. probably belonging to 
this species, but without the muscular indentation.—2547, 2 do. 
with very coarse corrugations. 
607. Purrura TRISERIALIS, Blainv. 
Monogr. Purp. in Nouv. Ann. Mus. p. 226, no. 53, (diagn. 
Gallic.,* tab. null.) 1832. 
es * As English naturalists are acquainted with the French language, it is 
thought that this description should be allowed priority, 
