TERRESTRIAL MOLLTJSCA INHABITING SOCIETY ISLANDS. 
25 
T. FALLENS, Pease. Plate III, fig. 43. 
Helix trochiformis, Gould (not of Per.), Expl. Ex. Shells, p. 61 (part). 
Helix Gressida, Schmeltz (not of Gould), Cat. Mus. Godeff., v, p. 95. 
Trochomorpha trochiformis, var. pallens, Pease, Jour, de Conch., 1810, p. 399; Proc. Zool. 
Soc., 1811, pp. 451, 414. 
Common, but very local on the trunks of trees at Tahiti and ]\Ioorca. It has 
usually been confounded with trochiformis, and was described by Mr. Pease as var. 
imllens. After a critical comparison of a large number of specimens from the al)Ove. 
mentioned localities with the Raiatea shells, I have separated it as a distinct, though 
closely allied, species. 
Shell umbilicated, rather solid, subtrochiform, obliquely and roughly striated, 
scarcely shining, yellowish white, with two narrow, revolving, reddish chestnut bands, 
the basal one the larger, and both submedian ; spire depressly conoid, witli nearly 
planulate outlines and rounded apex; suture with a narrow, depressed margin ; whorls 
six, slightly convex, slowly and regularly increasing, last one not deflected m front, 
acutely and compressly keeled, keel whitish ; base flatly convex, umbilicus narrow, 
about one-sixth the major diameter of the shell; aperture rhomboid-luniform ; peris- 
tome, above the keel, acute, straight, beneath the keel, gently arched, receding; 
incrassated at the base. 
Major diam. 16, height 9 mill. 
Hah . — Tahiti and Moorea. 
Var. a. Bands median, wide, blackish chestnut. Common. 
Var. h. Pale honey-yellow, with narrow reddish brown bands, which are frequently 
marginal. Somewhat rare and local. 
Var. c. Uniform whitish or yellowish white. Very rare. 
Var. d. Excepting the white keel and sutural margin, blackish che.stnut. Rather rare. 
As compared with the preceding species, it is more depressed, the whorls flatter, 
the base more planulate, the strim rougher and the columella more oblique and arched. 
The keel and sutural margin are white, and the aperture is more depressed. 
Examples of these shells sent to three good conchologists were by one referred to 
Gressida, Gld., by another to Apia, H. and J., and the third referred it to cxc7«va, 
Fer. I sent at the same time specimens of trochiformis, which were coiTCCtly 
determined. 
arelL, Gould, Proa ^ Soc. Nat. Hist., 1846, p. 176; Expl. Ex. Shells, p. 57, 
fig. 56. Pfeiffer, Mon. Hel., i, p. 123. 
Zonites Gressida, H. and A. Adams, Gen. Moll., n, p. 114. 
Nanina Gressida (Discus), Albers, Die Hel., ed. 2d, p. 62. 
Helix FoMae, Hombron and Jacquinot, Toy. Pol. Slid, PI. YU, gs. 
Helix exclusa, var., Pfeiffer (not of Fer.), Mon. Heb, iv, p. 115. 
Helix Swainsoni, var., Pfeiffer, Mon. Hel., iii, p. I5t. 
Much doubt and confusion exist in regard to Gould’s Helix Gressida, wind, he 
