INTRODUCTION. xix 
Fresawater Mo.ivsca.— Geographical Distribution (continued). 
GUATEMALA 
. 1 . Honpuras 
Mexico. (with abasco, Chiapas, AND NICARAGUA. Costa Rica} Panama. 
Yucatan, and SALVADOR. 
British Honduras), 
W. | Centr. E. N. | Yucatan, ls. w. W. HE Centr. | N.E.| W. 8. N. 
Belize. | (W.) and E. (W.) | (E.) 
Anodonta (cont.). 
( d. Scolianodon . .. 1 
| e. Euryanodon 2 1 
< f. Glabaris ........ _ 2 
| g. Pseudoleila ...... 1 
(hk. Pachyanodon .. 1 1 1 1? 
Mycetopus .......... 7 1 1 
Polymesoda. 
a. Polymesoda, s. str.| 2 1(2?) 2 1 1 - 1 
b, Egeta .......... 1 . 1? 1? 
Neocorbicula ........ 1 
Spherium .......... 1 2 1(2?)] 1 .. 1 
Hupera ............ . .. .. 1 .e 1 1 
Pisidium .......... 1 1 1 1 
FRESHWATER SHELLS CHARACTERISTIC OF Mexico AND CENTRAL AMERICA. 
Physa, sabgen. Aplecta, the species of larger size, ranging from Mexico to Peru. 
Cochliopa, from LNiSenta to Costa Rica. 
Pachychilus, with its four subgenera: Glyptomelania and Pachychilus, s. str., 
ranging trom Mexico to the northern part of South America, but absent 
from the West-Indian Islands; Oxymelania and Potamanaz, not reaching 
southward beyond N. Guatemala, but represented also in Cuba. 
Unio, subgen. Psoronaias, inhabiting South-eastern Mexico and Northern Guate- 
mala. 
The subgenera Arotonaias of Unio and Scolianodon of Anodonta are almost 
exclusively confined to the Lakes of Nicaragua and Managua. 
FRESHWATER SHELLS sHowiInG A Nearctic AFFINITY. 
The majority of the Limneide, chiefly the subgenus Alampetis of Physa, the 
subgenera Helisoma, Gyraulus, and Planorbula of Planorbis, and the species 
of Limnewa. All these are, so far as at present known, more abundant in 
Mexico and Guatemala than in Nicaragua or Costa Rica; Gyraulus, Planorbula, 
and Limnea extend, however, to the State of Panama. 
The somewhat doubtful Vivipara and the only Valvata, but limited to Mexico. 
c2 
