MAZATLAN UNIVALVES 173 
995. BULLA PNEBULOSA, Gould. 
U. S. Expl. Exp. Moll.—Mke. in Zeit. f. Mal. 1850, p. 162, 
no. 2. 
A very few thin, subglobose shells were found, with a small 
umbilicus, which are undistinguishable from the young of B. 
nebulosa; a species which, along with other points of simil- 
arity, shews the spirally striate umbilicus, and traces (though 
faint) of the rugosely striulate surface, of B. Adamsi. B. 
nebulosa is quoted from Guaymas, and may be one of the very 
few Californian species which cross the Gulf. I strongly sus- , 
pect however that these are but aberrant forms of the young 
B. Adamsi; which varies not a little in outline, solidity, and 
size of umbilicus. The adult shells are sufficiently distinct. 
Lengo. tat. 7: 
Hab.—Sta. Barbara, Nuttall.—San Diego, Lneut. Gireen.— 
Guaymas ; in sand, 12in.; Mus. Cuming.— Mazatlan ; Menke. 
—? Do. jun. extremely rare; L’pool Col. 
Tablet 788 contains the most characteristic specimen. 
226. Butta P?Quoyu, Gray. 
Sow. Thes. Conch. sp. 48, pl. 173, f. 71. : 
A very few small specimens were found, differing from B. 
Adamsi in the following points. Surface much more strongly 
and closely striulate ; outline flattened towards the umbilicus, 
at an angle of about 60°. Umbilicus strongly striate, bounded 
by a blunt angle. Long. °5, lat. °3. 
Hab.—Gallapagos, Cuming.—? Mazatlan; extremely rare ; 
DPpool Col. 
Tablet 789 contains 3 minute sp., probably belonging to this 
species.—790, the P adult specimen. 
227. BULLA EXARATA, 2. 8. 
B. t. parva, elliptica, compressa, aperturé elongata, angusta ; 
Suscd, epidermide tenwi cinctd; spiraliter tenuissime exarata, 
lineis plus minusve distantibus, in medio plerumque evanidis ; 
spird haud alte wmbilicata, intus striulis transversis divaricata ; 
labro postice producto ; labio columellam versus rimulam umbi- 
licalem simulante. 
Distinguished by the acuminated form, fine, rather distant 
spiral grooves, narrow produced aperture, and slight umbilical 
chink formed by a fold of the labium. The small spiral umbili- 
