PURPURELLA. 161 



Subgenus Purpurella, Ball. 



A section of the shell shows that the projections upon the 

 centre of the cohimella, are not mere tubercles, but regular spiral 

 ridges extending through nearly all the whorls. 



P. COLUMELLARTS, Lam. PI. 44, figs.3l, 35. 



Dark brown ; interior flesh color, the lips tinged with orange. 



Length, 1*5-3 inches. 



Mazatlan ; Gallapagos Isles. (Cuming.^ 



Carpenter remarks that, different as normal specimens of this 

 shell are from P. patula^ the labial callosity gradually vanishes in 

 some specimens, whilst the labral teeth are scarcely developed, 

 and the resemblance of the two species is then so great that they 

 can only be separated by a balance of characters. The series of 

 specimens before me confirm this view, and afford abundant 

 evidence of a common derivation however distinct they may be 

 typically. P. semi-imbricata, Lam., a species which has not been 

 identified, is perhaps equivalent to this species. 



P. leucostoma, Desh. (fig. 35), does not present any well-marked 

 distinctive characters ; it is quite young, being only 14 mill, in 

 length, and the coloration varies from the specimen figured to 

 that of P. columellaris. 



Subgenus Tribulus, Klein. 



P. PLANOSPIRA, Lam. PI. 45, fig. 32. 



Pale yellowish brown ; interior white, the revolving ribs within 

 the outer lip, and the basal ribs of the columella yellowish red. 

 The singular deep excavation of the middle of the columella is 

 crossed by an oblique black rib. Length, l*5-2'5 inches. 



Gallapagos Isles ; Lower California. 



P. APERTA, Blainv. Plate 44, fig. 30 



White, or yellowish white ; more or less stained with orange 

 upon the columellar tubercles and the teeth of the lip. 

 Length, 1*5-3 inches. 



W. Co. Central America. (Cuming.) Sandwich Isles. 

 Pease remarks that the species is peculiar to the latter locality. 

 21 



