452 MAZATLAN UNIVALVES 



GENUS POLINICES, Montf. 



Gray in Proc. Zool. Soc. 1847, p. 149, no. 185. 



Mammillaria, Swains, Treatise &c. p. 345, 1840. 



Mamma, (Klein) H. <$f A. Ad. Gen. vol. i. p. 210. 



Natica, pars, auct. Shell white, or slightly coloured, with a 

 strong parietal callosity. Operculum horny. The species of 

 this group are not yet satisfactorily ascertained ; and being 

 variable, yet with few distinctive characters, are very difficult 

 to define. 



576. POLINICES UBEE, Val. 



Natica uber, Val. Eec. Obs. Humb. 1833, vol. ii. p. 266. 



B. M. Cat. D'Orl. Moll. p. 33, no. 297. Phil in Kust. Mart. 



p. 60, sp. 65, pi. 10, f. 1. Eve. Condi. Ic. pi. 13, sp. 54. 

 ? Var.=Natica alabaster, Eve. Conch. Ic. pi. 9, f. 33, a, b. 

 Comp. Natica ovum, MJce. in Zeit.f. Mai. 1850, p. 165, no. 18. 

 Comp. ISTatica rapulum, Eve. Conch. Ic. pi. 12, f. 47, a, b. 

 Mamma uberina, H. fy A. Ad. Gen. i. 211. 



The extreme forms of this species are so dissimilar, as to 

 have warranted their separation. An examination of some 

 hundreds of specimens however shews that there is no con- 

 sistency in the types. The shell is either thin or heavy ; 

 subglobular or very transverse ; with the umbilicus quite open, 

 or reduced by the callosity to a mere chink ; the callus varying 

 greatly in shape and intensity. The callosity projects con- 

 siderably beyond the aperture, leaving a sutural groove. 

 Umbilicus more or less slightly spiral. The extreme open 

 form appears to be the N. alabaster, Eve. Menke's shell is 

 described as pellucid, with an opaque zone at the suture ; but 

 may be a thin representation of this species. The N. uni- 

 maculata, Eve. agrees almost exactly in form, but has a dark 

 spot on the callosity. The Mazatlan shells are pure white ; 

 with an extremely thin deciduous epidermis (of which traces 

 only were seen) ; and presenting the same habit of growth in 

 the smallest specimen, which is '36 long. The largest sp. (form 

 alabaster) measures long. 1'46, long. spir. '38, lat. 1*4, div. 110. 

 An elevated sp. '95, '28, '82,,, 90. 



Hab. Casma, Peru ; in muddy sand, 4 fm. ; Cuming. Callao, 



D 1 Orbigny. Mazatlan ; not uncommon ; L'pool Col. 



Tablet 2056 contains 4 sp. spreading form, open umbilicus. 

 (The largest is N. alabaster, .Zfoe.) 2057, 4 do. umbilicus more 



