172 SHELLS AND SHELL-FISH. PART I. 



this same thickening of the pillar into a central fold is 

 observable in Leucostoma, a name by which we now 

 designate a remarkable little shell (fig. 24.) of the 

 same shape as the more elongated 

 Achatinelloe, but with the addition 

 of a thick gibbous mass of white 

 enamel placed on the top of the 

 aperture within, where the outer 

 lip joins the body-whorl: this 

 little pad, in short, is exactly the same as what is seen 

 in Melanopsis, the base is distinctly emarginate, and 

 the outer lip thin ; but then the substance is more 

 like that of a marine than a land shell, and both the 

 interior of the aperture, and the outside of the whorls, 

 are transversely striated : the space between the upper 

 pad and the commencement of the plait on the pillar 

 is without) enamel, and is so short that it has the ap- 

 pearance of a deep notch : that this shell, however, 

 either by affinity or analogy, has a strong relation to 

 the types where we now place it, admits of little doubt ; 

 our difficulty lies in determining between these two 

 relations. If not a marine, it may be an amphibious 

 species ; in this respect it seems to have a relation of 

 analogy to Melanopsis, as well as one, more near, to 

 Planaxis. Achatenilla is our fifth and last type. These 

 little shells are remarkable for the beauty of their colours ; 

 they are all inhabitants of the Pacific Islands, where 

 they are used as bead-like ornaments. They are at 

 once known by the thickened rim on the internal part of 

 the outer lip : were this rim external, nothing but the 

 truncated pillar would prevent these shells being placed 

 with the Cyclostomce. With Achatinella, in fact, the 

 circle is closed Its connection to Achatina proper, with 

 which our survey began, is effected by that well-known 

 shell, the A. virginea, which is almost an aberrant 

 Achatinella : in this well-known species, the aperture 

 is very oblique, as in Achatinella pica, and the pillar, 

 like that shell, considerably turned inward. The thick- 

 ening on the inner margin of the outer lip is not 



