TERRESTRIAL MOLLUSCA IjSrHABITi:N'G SOCIETY ISLANDS. 
23 
taken in a large valley on the north side of Moorea, bnt at a much less elevation 
above sea-level. 
Its most important characters are its globose-conic form, rib-like striic, dark color, 
smooth base and delicate periphery-keel. It cannot be confounded with any other 
Polynesian species. 
T. Tahitensts, Garrett. Plate II, figs. 39, 39 a, 39 h, 39 c. 
Shell small, subperforated, depressed-turbinate, thin, subpellucid, above with tine, 
sharp, crowded, oblique, elevated striae, fidvous corneous ; spire dome-shaped, smooth 
and rounded at the apex; suture moderately impressed, margined above by the 
continuation of the periphery-keel ; base depressly convex, smooth, glossy, perforation 
punctiform, not deep ; whorls four and a half, flatly convex, regularlv increasing, 
last one narrow, not deflected in front, periphery with a prominent thread-like keel ; 
aperture slightly oblique, ovate-lunate ; peristome straight, acute, with distant margins ; 
columella with a large, white, tubercular nodule. 
Major diam. 2|, height 2 mill. 
Hub. — Tahiti. 
This, the smallest species inhabiting the group, was found adhering to the under 
side of loose stones at an altitude of 2000 feet, on the northw'est side of Tahiti. 
It is nearly the shape of suhrngosa, but is more rare, smaller, whorls flatti*r, spire 
more regularly dome-shaped, striae much finer, and the conspicuous columellar nodule 
will at once distinguish it. 
Genus ZONITES, jMontfort. 
Z. Mookeana, Garrett. Plate II, figs. 28, 28 a, 28 h. 
Shell small, perforated, orbicular, depressed, thin, pellucid, shining, faintly striah'd, 
whitish corneous ; spire convexly elevated ; suture faintly impressed, narrou ly mar- 
gined; whorls four, slightly,^convex, regularly and moderately increasing, last one 
somewhat depressed, not descending in front, rounded on the perii)liery ; bas(' 
depressly convex, deeply indented at the axis, which exhibits a small perforation ; 
aperture subvertical, orbicnlar-luniform ; peristome acute, straiglit, roundly curved, 
margins distant ; columella simple. 
Major diam. 4, height 2| mill. 
Of this small species I have five examples before me, all found associated with 
M. verticillata at Moorea. 
It can scarcely be ^distinguished from Vitiensis, except in being smaller, more 
polished, paler and the strise smoother. 
Genus TROCHOMORPHA, Albers.^ 
So far as I can ascertain, the Society Islands are the only group in Eastern Polynesia 
inhabited by the above genus. Dr. Pfeiffer, on the authority of Anton, cites Opara 
= Rapa as one of the localities of T. trcchiformis. If the genus occurs on that 
