CHOANOPOMA. 13 
phical extension of the species appears to be rather limited ; not one of those inhabiting 
Mexico and Central America is known to live also in the West-Indian Islands or in 
South America; and even within our limits each species is as yet known only from one 
province or, in a few cases, from two neighbouring ones. 
As the general facies of both genera (Choanopoma and Chondropoma) is very. much 
alike, and they are discriminated only by the structure of the operculum, we give on 
pages 14, 15 one comparative table for the species of both. 
CHOANOPOMA. 
Choanopoma, Pfeiffer, in Zeitschr. f. Malak. 1847, p. 45. 
This genus is characterized by the elevated edges of the whorls in the operculum ; 
the operculum itself is somewhat more circular than in Cyclostoma proper and in 
Chondropoma; the shell is generally ovate, with swollen whorls divided by deep 
sutures, pale-coloured, and sharply sculptured. For the distinctive characters of the 
species see the table on p. 14. 
a. Last whorl adhering to the preceding in its whole length. 
1. Choanopoma trochleare. 
Cyclostoma trochlea, Pfr. P. Z.S. 1851, p. 249°. 
Cyclostoma trochleare, Pfr. in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Cyclostoma, no. 315, 
p. 311, t. 41. figg. 7, 8°. 
Cistula (?) trochlearis, Pfr. Monogr. Pneum. Vivent. i. p. 275, & ii. p. 185°; Gray, Cat. Phaneropn. 
p. 194°. Xl 
Chondropoma trochleare, Reeve, Conch. Icon. xiv., Chondropoma, t. &. fig. 82°. 
Var. majus. 
Choanopoma chiapasense, Fischer & Crosse, Miss. Scient. Mex., Mollusca, i. t. 41. fig. 8 (letter- 
press not yet published) °. 
Hab. Cutapas® ° (Ghiesbreght *). 
The original locality was unknown to Pfeiffer '. 
2. Choanopoma sumichrasti. 
Choanopoma sumichrasti, Crosse & Fischer, in Journ. de Conch. xxii. p. 283 (1874)'; Pfr. Monogr. 
Pneum. Vivent. iv. p. 1567; Fischer & Crosse, Miss. Scient. Mex., Mollusca, u. t. 41. 
fig. 9 (letterpress not yet published). 
Hab. S.W. Mexico: Isthmus of Tehuantepec (Swmichrast ' *). 
