AS MOLLUSCA. 
HELIx caLcuLosa (Gould). 
Testa parvula, hyalina, fragilis, nitida, laevigata, cornea, globoso-pyra- 
midalis: spira depressa, anfractibus quatuor convextusculis, ad pert- 
pheriam angulata et tenuissimé carinata: infra convexa, regione um- 
bilicali impressa sed imperforata: apertura lunata ; labro simplict, 
margine interna rotundata. 
SHELL minute, hyaline, fragile, corneous, depressed globose, pyra- 
midal, shining, smooth; whorls four, convex, with a distinct and 
closely margined suture, forming a low, obtuse, pyramidal spire: 
beneath nearly as convex as above, somewhat pitted at the centre, but 
not perforated: periphery obtusely angular and carinated: aperture 
rather small, lunate, with the columellar portion forming a pillar of 
considerable length : lip simple. 
Diameter one-tenth of an inch; axis a little less. 
Inhabits Tahiti. Couthouy. 
Like H. chersina, Say, but has an angular periphery, though it is 
less angular than H. subtilssima. 
Figures 63, 63a, 63, three views of the shell, enlarged; 63c, 
natural size. 
HeELix susrinissima (Gould). 
Testa minuta, fragilissima, nitidissima, lenticularis, plano-convexa, 1m- 
perforata: spira planulata, anfractibus quinque planis, arcte volutis ; 
ultimo acutissimé carinato: apertura (fracta). 
Helix subtilissima, Goutp; Proceed. Boston Soc. Nat. Hist., ii. 177. 
Nov. 1846. Expedition Shells, 24. Preirrer; Monog. Helic., i. 231. 

SuELL very fragile, discoidal above, sharply carinated at periphery, 
obversely conical beneath, imperforate, hyaline. There are five closely 
revolving, flat whorls, marked with exceedingly fine lines of growth. 
The aperture is fractured, so as to afford no definite outline. 
