HELIX - THELIDOMUS. . 57 



Section THELIDOMUS Swainson. 



Thelidomus SWAINS., Shells and Shell-fish, p. 330, 1840. (not 

 Thelidomus SWAINS., I. c., p. %53,=Helicopsyche Brem., 1848 ; larva- 

 cases of a neuropterous Arthropod). Otala BECK, Index, p. 35. 

 (1837). MORCH, Cat. Yoldl, p. 12, H. and A. AD., Gen. Rec. 

 Moll, ii, p. 197. (not of SCHUM.) Pachystoma ALBEES, Die Heliceen, 

 1850, p. 125. (not Pachystoma GUILDING, Zool. Jo-urn., p. 536, 1828, 

 Atypical Ampullaria.) 



Thelidomus exhibits a certain likeness to the Canary Island group 

 Hemicycla. The species fall into two sections; (1) variegated, 

 granulate species, inhabiting Jamaica, Porto Rico and the lesser 

 Antilles, and (2) straw-colored or light russet forms confined (with 

 one exception) to Cuba. The latter section is capable of being sub- 

 divided into two natural groups, founded upon the presence or ab- 

 sense of microscopic spiral incised lines upon the shell. The species 

 of the second division, without spiral lines, belong for the greater 

 part to the Eastern extremity of the Island. They form a very 

 homogeneous assemblage ; and hair-splitting has been resorted to 

 by authors to keep up the specific lines. I have given distinctive 

 characters which will enable the student to identify most specimens ; 

 but in the group of auricoma, bayamensis, provisoria, there occur 

 forms nearly or entirely intermediate. 



Shell generally variegated ; rugose or granulate. Species of Jam- 

 aica, Porto Pico and the lesser Antilles. 



H. INCERTA Ferussac. PI. 4, figs. 36, 37 ; pi. 1, figs. 1, 2. 



Imperforate, globose-depressed or subconoidal, opaque, lusterless, 

 light yellow, with numerous narrow longitudinal streaks and few or 

 many interrupted spiral bands of dark chestnut color or umber; ir- 

 regularly, inconspicuously obliquely striate, the whole surface cover- 

 ed with a more or less obvious rather coarse, often subobsolete 

 granulation ; spire elevated or depressed, the apex and inner whorls 

 light corneous, nearly smooth, but slightly convex, the outer one or 

 two whorls more convex, separated by deeper sutures ; whorls 4, the 

 last rounded, never carinated, a little deflected toward the aperture, 

 convex below ; aperture oblique, wide-semi lunar, white within ; 

 outer lip narrowly and slightly expanded, baso-columellar margin 

 very oblique, expanded, wide, adnate to the base, thickened within 



