478 MAZATLAN UNIVALVES 



Whether or not the Pacific specimens of the hsemastomoid 

 type are distinct from the Atlantic, is not yet agreed upon by 

 naturalists. That the Mazatlan specimens are eonspecific, I 

 cannot doubt after a careful scrutiny of more than 500 speci- 

 mens. TThether the Lamarckian P. bicostalis be the \V est 

 American shell, as supposed by Keeve, or the E. Indian, as 

 decided by Blainville, cannot be determined by his diagnosis. 

 But as the W. coast shells were scarcely known in Lamarck s 

 days (except those brought by Humboldt & Bonpland, which 

 are specified as such,) when there is a doubt, it seems fair to 

 give the benefit of it to the old East and West Indian species. 

 Supposing the local forms to be distinct, it is proposed to 

 retain Blainville's name for the W. American shells ; leaving 

 the P. bicostalis for the E. Indian, P. hajmastoma for the 

 European, and P. Floridana for the W^. Indian t-v^es. The 

 P. undata of Lam. is abnost certainly the W. Indian species 

 (not htemastomoid) well figured (among others) by Kiener. 

 This does not occur on the West Coast. The Mazatlan sheUs 

 are either (1) very depressed, like P. deltoidea, thick, of a 

 uniform gray colour, with distant coarse spiral stria?, stout 

 tubercles, and whoUy orange mouth, (P. consul of mnlce not 

 Lam) : or ^2) abnost wholly assuming the usual appearance 

 of P. htemastoma : or (3) of a Buccinoid shape, with very faint 

 tubercles, richly variegated brownish colour, shewing at the 

 mouth, and comparatively thin texture, (P. undata of Val. not 

 Lam.) : or (4) of the same shape, with stout tubercles, and 

 back richly coloured, as described by Eeeve under P. bicos^lis. 

 Barely the shell is almost wholly of a reddish brown. \\ hen 

 painted, the pattern is extremely various, being laid on some- 

 times in irregular patches, sometimes in variegated threads 

 between the spiral stria?. These varj- in width and depth, but 

 are never so close as in the specimens observed from the 

 Atlantic. Mr. Hanley has also pointed out that the strise are 

 punctured ; an appearance due to the intersection of famt 

 stria? of growth, which follow the crenatcd form of the mouth, 

 and often are but faintly discernible in the coarsely grooved 

 comulo\di specimens. The mouth is often nearly smooth and 

 ^vhite within, till near the labnmi, where orange develops, 

 with spiral ridges sometimes displaying an inner row of tuber- 

 cles But sometimes (especially when young.) it is deeply 

 lirate over the whole siirface, which is brown, while the swollen 

 ribs are light yellow. The labium has always more or less ot 

 an orange deposit, wrinkled near the base, and with an intra- 

 Butural rib. There are five smooth apical whirls, sometunes 



