24 terrestrial mollusca inhabiting society islands. 
smnll island which I very much doubt, the species is distinct from the Society Island 
she'll!. Mr.’ Gloyne, in his very valuable paper on the “ Geographical Distribution of 
Terrestrial Mollusca ” (Quar. Jour. Conch., i, p. 315), erroneously assigns three species 
of Tro,J.<ymorpha to the Cook’s Islands, where tlie genus does no occur He is also 
wroim in referring the genera Palaina, Gychmorpha and djdophorns to that group. 
In the Society Islands all the Trochomorplne are peculiar to the group, and occui 
on all the islands except Borabora and Maiipiti. Having personally collected severa 
thousand specimens at the five islands inhabited by the genus, and after a thorough 
study and critical comparison with numerous species from the various islands in the 
Western Pacific, I do not hesitate to assign five species to the group. One restricted 
to Tahiti, one to Hiiaheine, two common to Raiatea and Tahaa, and one common to 
Tahiti and Moorea. 
T. TROciiiFORMis, Ferussac. 
Helix trochiformis (Hellicella), Ferussac, Prod., p. 301. Pfeifler, Symb., ii, p. 40; Mon. 
Hel., 1 , p. 206. Chemnitz, ed. 2d, No. 68, p. 13, figs. 1, 8. Gould, Expl. Ex. Shells, p. 61 
(part). Reeve, Conch. Icon., No. 606, PI. CYIII, fig. 606. 
Trocliomorpha trochiformis, Albers, Die Ilel., p. 116. Pfeiffer, Yers., p. 133. Pease, Jour, 
de Conch., 1811, p. 398; Proc. Zool. Soc., 1811, pp. 456, 414. 
Zonites trochiformis {Trochomorpha), H. and A. Adams, Gen. Moll., ii, p. 115. 
Nanina trochiformis ( Trocliomorpha), Albers, Die Hel., ed. 2d, p. 60. (Discus) Paetel, Cat. 
Conch., p. 85. 
This very variable species lives on the trunks of trees and is restricted to Raiatea 
and 'I’ahaa. Dr. Pfeiffer, on the authority of Anton, erroneously cites Tahiti and 
Opara = Rapa as its habitat. It is scarcely necessary to add that Fcrussac’s locality, 
“ Isle de France,” is also erroneous. 
It is subject to more variation than any other known species. The usual proportion 
of height to the greatest diameter is 10 by 16, and the extreme variation 12 by 14 
and 9 by 14 mill. The umbilicus is deep and narrow. M^horls six, convex, conspicu- 
ously margined, last one with a compressed periphery-keel. Base rather strongly 
convex, and Pfeiffer’s “ margine columellari recte descendente ” is a well-marked 
feature in se])arating it from the nearest allied species. The color is yellowish brown, 
honey-yellow, more rarely orange-yellow, with a dorsal and basal deep brown-black, 
generally .sharply defined band. The dorsal band which occupies the lower half of 
the wliorls is narrower than the basal one, which latter is submarginal. The acute 
periphery-keel is pale straw-yellow. Occasionally the bands arc diffused OA’er the 
whole width of the whorls, except the keel and sutural margination. A more rare 
variety occurs of a pale greenish yellow, with the bands nearly or quite obsolete. 
Uniform honey-yellow specimens are also very rare. 
Hybrids between this species and Swamsomi are not infrequent, and arc more 
depressed, the umbilicus more open and the columella more obliquely curved than in 
the normal condition. Mr. Pease may have mistaken these hybrids for Gould’s 
