104 MOLLUSCA. 
Axis and diameter two-fifths of an inch. 
Inhabits Upolu. Couthouy. 
Differs from C. str7gatum in its more elevated, acutely conical form, 
its plaited whorls without prominent revolving lines, its rounded 
periphery and base, and its more contracted umbilicus. The young 
are also discoidal, without folds, but with rather strong, somewhat 
nodular spiral lines, and the colour is of a bright beryl green. 
Figure 118, shell with the animal; 118 a, 118 8, top and base of the 
shell. 
CycLosToMa OBLIGATUM (Gould). 
Testa parva, crassa, sub-globosa, cinerea, arcté perforata, utrinque sulcis 
et costulis acutis sub-crenulatis equalibus cincta, et linets incrementi 
subtilissimis striata: spira acuta, anfractibus quinque rotundatis : 
apertura parva, ovata ; peristomate simplici, crasso. 
Cyclostoma obligatum, Gouin ; Proceed. Boston Soc. Nat. Hist., 11. 
205. March 1847. Expedition Shells, 38. 
Suet small, very thick and solid, ovate-globose, of an ashy-white 
colour; the whole shell is sculptured with raised, revolving threads, 
and intervening grooves of about equal size; the threads or ribs are 
somewhat sharp, and with an edge slightly scolloped. There are five 
rounded whorls, forming an acute spire: the base is convex and 
polished ; the aperture very small, about half the length of the shell, 
and of an ovate form, being acute posteriorly: lip thick and rounded. 
Umbilicus very small. 
Length three-eighths of an inch; breadth one-third of an inch. 
Inhabits Metia Island. Couthouy. 
Still smaller than C. phcatum, and remarkable for its solid structure, 
its alternate coarse ridges and grooves, and its small, ovate aperture. 
It looks not unlike some specimens of Lettorina rudis. 
