452 MAZATLAN UNIVALVES 
Genus POLINICES, Monff. 
Gray in Proc. Zool. Soc. 1847, p. 149, no. 185. 
Mammillaria, Swains, Treatise &c. p. 345, 1840. 
Mamma, (Klein) H. & 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 dificult 
to define. 
576. PoLINIcEs UBER, Val. 
Natica uber, Val. Rec. Obs. Humb. 1833, vol. ii. p. 266.— 
B. M. Cat. D Orb. Moll.p. 33, no. 297.— Phil. in Kust. Mart. 
p. 60, sp. 65, pl. 10, f. 1— Rve. Conch. Ic. pl. 13, sp. 54. 
P Var.=Natica alabaster, Rve. Conch. Ic. pl. 9, f. 33, a, b. 
Comp. Natica ovum, Whe. in Zeit. f. Mal. 1850, p. 165, no. 18. 
Comp. Natica rapulum, Rve. Conch. Ic. pl. 12, f. 47, a, b 
Mamma uberina, H. & 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, Rve. 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, Rve. 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. pee) OoE a IBF) ae. eon aa noo 
Hab.—Casma, Peru ; in muddy sand, 4 fm. ; Cuming.—Callao, 
D Orbigny.—Mazatlan ; not uncommon; L’pool Col. 
Tablet 2056 contains 4 sp. spreading form, open umbilicus. 
(The largest is N. alabaster, Rve.)—2057, 4 do. umbilicus more 
