56 HELIX THELIDOMUS. 



graphia, v, p. 50. H. brocheroi Gutz., ARANGO, Fauna Mai. 

 Cubana, p. 64. 



Like no other species in the elevated Bulimus-like form. 



Group XIII. THELIDOMUS Swainson. 



A group of large, semiglobose snails, confined to the West Indies 

 in distribution. And allied in the characters of both shell and 

 animal to the succeeding groups (Caracolus, etc.) not to the preced- 

 ing (Hemitrochus, etc.), which belong with the great group compri- 

 sing most of the banded snails of Europe and the Americas, such as 

 Poinatia, Arionta, Lysinoe, Odontura, Tachea, etc. 



The shell in the present group is generally rather large, not much 

 variagated, nor bright in color, usually granulated, decussated, or 

 at least, strongly costulate. The aperture is generally large, not 

 obstructed by teeth, though often narrowed by a basal callus. The 

 axis is usually imperforate ; the periphery is rounded, except in a 

 few species. 



This group is composed of part of the elements of Ferussac's 

 Helicogena. It is equal to the subgenus Helicogena of Fischer only 

 in part ; for I have been obliged to dismember that group as con- 

 stittued by him (Manuel de Conchyl., p. 471), placing Cory da, His- 

 trio and Dialeuca in my group Hemitrochus, and Oxychona in the 

 immediate neighborhood of Caracolus. 



Synopsis of Sections. 

 Section THELIDOMUS Swainson, 1840. 



Shell globose-depressed, with 4J or less whorls, the last deflected 

 at the aperture, rather gibbous beneath, carinated or rounded at the 

 periphery ; surface costulate, granulated or decussated ; aperture 

 very oblique ; peristome more or less expanded, thickened within, 

 lower margin straightened, with a plate-like callus inside, its edge 

 sometimes toothed. Type, H. incerta, Fer. 



Section PARTHENA Albers, 1850. 



Shell globose or depressed, whorls rapidly widening, the last large, 

 carinated or rounded at the periphery ; surface visibly or micros- 

 copically granulated; aperture large; peristome expanded, col- 

 umellar margin more or less arcuate, never dentate, nor with a plate- 

 like callus within. Type, H. angulata Fer. 



