248 Bulletin American Museum of Natural History [Vol. LIII 
Melaniidz 
(THraripa of some authors) 
Shell spiral, varying widely in shape, but typically turrited or ovate and imper- 
forate, covered with a distinct periostracum, the aperture ovate and entire or notched 
basally. Operculum spiral, at least in its early stage. 
Muzzle wide, emarginate in front. Tentacles subulate, the eyes at their outer 
bases. Foot short. No external male organ. Respiration branchial. The radula has 
3-1-3 teeth, their cusps with few or many denticles. 
These mollusks inhabit fresh or rarely brackish water in tropical 
and temperate parts of the world. 
The extensive and heterogeneous family of melanians or Thiaride 
can hardly be technically defined so as to exclude all Cerithiide, except 
by taking its usually fresh-water station into account. As Bouvier has 
remarked, the melanians are the fresh-water and the cerites the marine 
phase of a single large group. There has been extensive differentiation 
throughout both branches of this group, and there appears to be closer 
relationship between certain members of the fresh-water and marine 
branches than between divergent lines of the latter. 
The first definite steps towards a natural classification of the 
melanians were taken by Troschel. The arrangement of Fischer and 
Crosse! is an expansion of Troschel’s ideas, incorporating the results of 
later investigation. ‘The subfamilies recognized by them appear to be 
natural groups, which will probably be admitted as families eventually. 
Three subfamilies or families occur in the Ethiopian Region. 
1. Melaniine (or Melaniide proper), with fringed mantle border; 
the radula small, with plain central tooth; operculum paucispiral, 
with baso-columellar nucleus. Old World. African genera: Melania 
Melanoides, Pachymelania. | 
2. Potadomine (or Potadomidee),? in which the mantle margin is 
plain; the radula relatively large, with central tooth swollen mesially 
below the cusp; cusps of all teeth with few denticles. Operculum from 
paucispiral with basal nucleus to multispiral with central nucleus 
(though never with many whorls). Tropics of both hemispheres. African 
genera: Potadoma (and perhaps Rhinomelania). 
3. Paludomine (or Paludomide), with fringed mantle margin, 
plain central tooth of the radula, the operculum concentric with spiral 
nucleus about midway between its ends, or lamellar with external or 
11891-1892. ‘Miss. Sci. au Mexique, Etudes Moll. Terr. et Fluv.,’ II, pp. 311-318. 
2We prefer to base this subfamily on Potadoma, the oldest genus, rather than on Pachychilus, a 
later genus, the name of which has to be changed on account of the earlier term Pachycheilus in Am- 
pullariide. The term Melanoidide or Melanoidine of H. von Ihering (1909, Journ. de Conchyl., 
LVII, pp. 296 and 298), though equivalent to Pachychiline Fischer and Crosse, i i 
since the genus Melanoides does not belong to this group. Bee ate, 
