- KEY TO FAMILIES. T 
fresh waters of all parts of the world. It is 
numerously represented in the United States. 
Order SCUTIBRANCHIATA. 
Sub-order Podopthalma. 
Includes marine, and a few fluviatile species 
(Neretine). Head furnished with to tenta- 
cles and with eyes on separate pedicels. Shell 
spiral, operculate. 
Family Neriripz. 
Shell generally semi-globose, spiral of few 
whorls, not umbilicated. Cavity simple from 
the absorption of the internal portions of the 
whorls. 
Distribution tropical and sub-tropical. 
Order PECTINIBRANCHIATA. 
Sub-order Rostrifera. 
Includes marine and fluviatile species. Head 
with a produced, contractile rostrum. Tenta- 
sles subulate. 
