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, *58, 1-64, 100. 



An elevated sp. 2'35, '85, 1-6, 70. 



Hob. Acapulco, Humboldt fy 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 <$f 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. 



4~ 607. PUBPUBA TBISEBIALIS, Blainv. 



Monogr. Purp. in Nouv. Ann. Mus. p. 226, no. 53, (diagn. 

 Gallic.;* tab. null.) 1832. 



* As English naturalists are acquainted with the French language, it is 

 thought that this description should be allowed priority. 



