INTRODUCTION. XVli 
(subgen. Oxychona, infra); Eucalodium and Celocentrum, southward to Guatemala; Holo- 
spira, from Arizona and Texas to South-west Mexico and Yucatan; Pseudosubulina ; 
Xanthonyx, from Misantla to Chiapas. 
bb. Represented in the West-Indian Islands. 
Macroceramus (Guatemala). 
&. Extending into the greater part of North and South America. 
Glandina, Lysinoé (as restricted in this work): both absent from the West-Indian Islands. 
B. Essentially West-Indian. 
Choanopoma, with Adamsiella, scarcely extending to South America, absent from North America ; 
Chondropoma, with Cistula, extending to South America, absent from North America; 
Helicina, extending a little north of the Mexican frontier and still further in South America ; 
Spiraxis. 
C. Prevailing North-American. 
a. Scarcely represented in the West-Indian Islands. 
Omphalina, southward to Guatemala; Polygyra, southward to Honduras; Pupa, with Vertigo and 
Leucochilus, southward to Nicaragua and (subgen. Leucochilus) to Panama (somewhat cosmo- 
politan) ; Pupoides, southward no farther than Central Mexico. 
b. Not represented in the West-Indian Islands. 
Strobila, southward to North Guatemala; Rhadbdotus (group of Bulimulus dealbatus), southward to 
the Isthmus of Tehuantepec. 
D. Prevailing South-American. 
a. Represented in the West-Indian Islands. 
Cyclotus (Neocyclotus) ; Cyclophorus (Amphicyclotus) ; Ortalichus; Otostomus; Bulimulus, subgen. 
Leptomerus ; Simpulopsis ; Leptinaria. 
b. Essentially South-American, and not represented in the West-Indian Islands. 
Labyrinthus, to as far north as Costa Rica; Solaropsis, to as far north as N. Guatemala. 
BIOL. CENTR.-AMER., Terr. and Fluviat. Mollusca, May 1901. C 
