TERRESTRIAL MOLLUSCA INHABITING SOCIETY ISLANDS. 25 
T. PALLENS, Pease. Plate III, fig. 43. 
Helix trochiformis, Gould (not of Fer.), Expl. Ex. Shells, p- 61 (part). 
Helix Cressida, Schmeltz (not of Gould), Cat. Mus. Godeff., Wg de KE 
Trochomorpha trochiformis, var. pallens, Pease, Jour. de Conch., 1870, p. 399; Proc. Zool. 
Soc., 1871, pp. 457, 474. 
Common, but very local on the trunks of trees at Tahiti and Moorea. It has 
usually been confounded with ¢rochiformis, and was described by Mr. Pease as var. 
pallens. After a critical comparison of a large number of specimens from the above- 
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, with nearly 
planulate outlines and rounded apex ; suture with a narrow, depressed margin ; whorls 
six, slightly convex, slowly and regularly increasing, last one not deflected in 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. 
Hab.—Tahiti and Moorea. 
Var. a. Bands median, wide, blackish chestnut. Common. 
Var. b. Pale honey-yellow, with narrow reddish brown bands, which are frequently 
marginal. Somewhat rare and local. 
Var. ¢. Uniform whitish or yellowish white. Very rare. 
Var. d. Excepting the white keel and sutural margin, blackish chestnut. Rather rare. 
As compared with the preceding species, it is more depressed, the whorls flatter, 
the base more planulate, the stri 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 
Cressida, Gld., by another to Apia, H. and J., and the third referred it to exclusa, 
Fer. I sent at the same time specimens of trochiformis, which were correctly 
determined, 
T. Cressipa, Gould. 
Helix Cressida, Gould, Proc. Bost. Soc. Nat. Hist., 1846, p. 176; Expl. Ex. Shells, p. 57, 
fig. 56. Pfeiffer, Mon. Hel., i, p. 123. 
Zonites Cressida, H. and A. Adams, Gen. Moll., ii, p. 114. 
Nanina Cressida (Discus), Albers, Die Hel., ed. 2d, p. 62. 
Helix Vahine, Hombron and Jacquinot, Voy. Pol. Sud, Pl. VII, figs. 1-4. 
Helix ewclusa, var., Pfeiffer (not of Fer.), Mon. Hel., iv, p. 115. 
Helix Swainsoni, var., Pfeiffer, Mon. Hel., iii, p. 157. 
Much doubt and confusion exist in regard to Gould’s Helix Cressida, which he 
