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 conspecific, I 

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

 mens. Whether the Lainarckian P. bicostalis be the West 

 American shell, as supposed by Reeve, 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. hsemastoma for the 

 European, and P. Floridana for the W. Indian types. The 

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

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

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

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

 uniform gray colour, with distant coarse spiral strise, stout 

 tubercles, and wholly orange mouth, (P. consul of Menlce not 

 Lam.) : or (2) almost wholly assuming the usual appearance 

 of P. hsemastoma : 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 Vol. not 

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

 back richly coloured, as described by Reeve under P. bicostalis. 

 Rarely the shell is almost wholly of a reddish brown. When 

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

 times in irregular patches, sometimes in variegated threads 

 between the spiral striae. These vary 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 faint 

 strise of growth, which follow the crenated form of the mouth, 

 and often are but faintly discernible in the^ coarsely grooved 

 comuloid specimens. The mouth is often n*early smooth 

 white within, till near the labrum, where orange develops 

 with spiral ridges sometimes displaying an inner row of tube 

 cles. But sometimes (especially when young,) it is deepl; 

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

 ribs are light yellow. The labium has ahv ays more or less < 

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

 sutural rib. There are five smooth apical whirls, sometimes 



