452 MAZATLAN UNIVALVES 



Genus POLINICES, Montf. 



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



MammiUaria, Swains, Treatise &c. p. 345, 18^. 



Uamma, (Klein) H. Sc A. Ad. Gen. vol. i. p. 210. 



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

 strong parietal caUosity. Operculum horny. The species of 

 this group are not yet satisfactorily ascertained; and bemg 

 variable, yet with few distinctive characters, are very diihcult 

 to define. 



576. POLINICES UBEE, Val. 



Natica uber, Val. Bee. Ohs. Hicml. 1833, vol. ii- P; 266.- 

 B M. Cat. B'Orb. Moll. p. 33, no. 297.— Phil, in Kust. Mart. 

 p. 60, sp. 65, pi. 10, f. l.-Bve. Conch Jr pi. 13 sp. 54. 

 P Var. = ]Sratica alabaster, Bve. Conch. Ic. pi. 9, t. 66, a, b. 

 Comp. Natica ovum, Mice, in Zeit.f. Mai. 1850, p^l6o, no. 18. 

 Comp. Natica rapulum, Bve. Conch. Ic. pi. 12, f. 4/, a, b. 

 Mamma uberina, S. <^ A. Ad. Gen. i. 211. 



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

 have warranted their separation. An examination oi some 

 hundreds of specimeQs however shews that there is no con- 

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

 subglobular or very transverse ; with the umbihcus quite open, 

 or reduced by the callosity to a mere chink ; the callus varj-mg 

 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, Bve.Men\e, sheU 8 

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

 may be a thin representation of this species, ihe ^•^\- 

 maculata, Bve. agrees almost exactly m form, but has a dark 

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

 with an extremely thin deciduous epidermis of which tracers 

 only were seen) ; and presenting the sanie habit of growth m 

 the smallest specimen, which is "36 long. The lajrgest sp (torm 

 alabaster) measures long. r46, long. sjnr. 'Z8, lat. l'i,div. IW. 

 An elevated sp. „ -95, „ '28, „ bi, ,, yu . 



^a6.-Casma,Peru; in muddy sand, 4 fm. ; Cunung-C^iao, 

 D'0/-&?>H J/.— Mazatlan; not uncommon ; Lpool. Lot. 

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

 (The largest is N. alabaster, i?.e.)-2057. 4 do. umbihcus more 



