MAZATLAN UNIVALVES 



Var. <?.=Natica Chemnitzii, Pfr. in Mart. Conch, p. viii.* 



C. J5. Ad. Pan. Shells, p. 201, no. 295. "N. Chemnitzii, 



Mke." Rve. ms. in Mm. CWw. (Non IS". Chemnitzii, Mke. 



loc. cit. 1849, p. 36. Nee Eed. Voy. Son. in J5. 3^. C^. 



p. 22, no. 168: =Neverita Chemnitzii, H. Sf A. Ad. Gen. 



i. 208.) 

 + ]STatica Pritchardi, Forbes, Proc. Zool. Soc. 1850, p. 272, 



pi. 11, f. 2 a-c. 



P-rNatica iostoma, Mice, in Zeit.f. Mai. 1847, p. 178, no. 5. 

 Comp. Natica tessellata, Phil, in Zeit. f. Mai. 1848, p. 158, 



no. 20. (Hal. ? ) 



The West-coast shells are extremely variable in size and 

 colouring, also in the tumidity of the whirls and elevation of 

 the spire. The Mazatlan specimens belong to a small, highly 

 coloured variety, which, with the less coloured larger shells, 

 was described by Prof. Forbes as JN\ Pritchardi. On comparing 

 these with a series from W. Mexico, collected by Lieut. Freere, 

 and another from the Gambia coast collected by Chief Justice 

 Hankin, in the Bristol Museum, also with the series from 

 various localities in the British Museum and the Cumingian 

 Collections, it does not appear that the local types are suf- 

 ficiently distinct to be accounted as separate species. The 

 Gambia specimens go through the same variations of colour as 

 those from W. Mexico. The Mazatlan shells much more closely 

 resemble the ordinary Gambia type than the ordinary West 

 Mexican type. They are however generally rather flatter in 

 the spire, with the subsutural wrinkles rather stronger, and 

 the operculum not indented in the inner surface. 



The operculum is thin, shelly, flat or very slightly concave ; 

 with a narrow, not prominent, rounded ridge along the outer 

 margin, and another small one bounding the part correspond- 

 ing to the umbilical callosity. The whole surface is very finely, 

 scarcely perceptibly, spirally striated : at the base rough and 

 callous ; the inner margin thickened, and very scabrous. The 

 operculum of the Californian form is rather swollen, smooth, 

 glossy, with the outside ridge scarcely seen ; the reflex area of 

 the callosity scarcely excavated, and the inner margin but 

 slightly roughened* It differs from the Gulf type, much more 

 than this does from the Gambian, 



* For justification of the above synonyms, v. the elaborate article of Koch and 

 the observations of Dunker. If the W. American sheDs should prove distinct, 

 the name Chemnitzii has precedence over that of Forbes, having been described 

 from Mexican specimens, although Menke applies the synonym to African shells. 



