GASTEROPODA. 53 
b. Smaller, depressed specimens, more or less coarsely ribbed, 
striated and mottled both above and below. 
Diameter one-fifth of an inch; axis one-tenth of an inch. 
Dr. Pfeiffer has given to this form the name of H. Jacquinott. 
In some specimens the whorls are somewhat deranged in their 
volution, so that the inner ones form a flat disc, while the two outer 
ones are placed one directly above the other. This variety, as well 
as the shell in an immature stage, have been described as distinct 
species ; but the examination of an extensive series, shows the im- 
propriety of this. Sometimes one or more of the lamelle are unde- 
veloped. In most specimens there are no revolving strie, but in some 
they even predominate over the coarse, radiating lines. Dr. Pfeiffer 
has recently described this as a distinct species, by the name of H. 
coarctata. 
From Tahiti and Eimeo, at 2000 to 5000 feet elevation. Couthouy. 
Figure 52, shell with the animal ; 52 a, the aperture, enlarged ; 52 6, 
depressed variety with the animal; 52c, the side, and 52d, the base 
of the distorted variety, enlarged; 52e, natural size; 52f, 52g, 52h, 
three views of the normal form, enlarged ; 527, natural size ; 52 k, 52 J, 
views of the young shell, the aperture enlarged ; 52 m, natural size. 
Hetix opouus (Gould). 
Testa parva, discoidea, deorsum compressa, supra planulata, infra con- 
cava, radiatim minutissimée et inequaliter striata, fusco-ferruginea, 
piceo tessellata: spira anfractibus quinque cum dimidio, supra exca- 
vatis, ultimo superné costato-carinato: apertura sub-rhombotdea ; 
Sauce lamella unica secundum anfractum penultimum instructd. 
Helix obolus, Goutp; Proceed. Boston Soc. Nat. Hist., ii. 175. 
Sept. 1846. Expedition Shells, 22. Preirrer; Monog. Helic., i. 184. 
SHELL small, discoidal, very much depressed, flat or concave above, 
shallow, basin-shaped beneath, with a rib-carina at the periphery, on a 
level with the upper plane ; colour rusty brown, tessellated alternately 
with dark chestnut brown. Whorls five and a half, separated by a 
14 
