D88 Bulletin American Museum of Natural History [Vol. LIII 
This group comprises 19 genera with 56 forms, no less than 44 being 
endemic, the last figure especially being surprisingly high. ‘There 1s, 
however, no difficulty in showing that all these mollusks are closely 
allied to the usual Ethiopian fluviatile species. In some cases, as in 
Lymnexa, Bulinus, Physopsis, Pila, and Lanistes, it is even somewhat 
doubtful whether the Tanganyikans are really separable from the more 
widely distributed forms. But others, such as Melanoid2s admirabilis, 
the species of Cleopatra and Corbicula, and Iridina speki, are quite 
peculiar and among the most characteristic animals of the lake. Some 
of them are distinguished from their Ethiopian relatives by the unusual 
large size and thickness, the bright coloration, or the elegant sculpture. 
So far as we are informed, most, if not all, of the mollusks of this 
group live in the quiet lagoons, marshes, or swamps of the shore, where 
sand spits shelter them against the mechanical action of the waves, and 
where fresh water drained from the coastal highlands tends to lower the 
normal salinity of the lake water. Under such favorable conditions they 
are frequently found in flourishing colonies. 
(2) The second group comprises a number of strictly endemic genera, 
but whose affinities to the usual Ethiopian fresh-water genera are still 
beyond dispute. 
*Neothauma tanganyicense *Grandidierta hautteceurt 
*Neothauma tanganyicense var. bicarina-  * - incarnata 
tum a es mura 
*Neothauma tanganyicense*var. euryom- _* % rhynchonella 
phalum | i ee rotundata 
*Neothauma tanganyicense var. major a smithr 
*Mysorella (2?) multisulcata * . tanganyicensis 
* Melamia”’ tanganyicensis * s és var. exalbida 
*Grandidieria burtona t h thomsoni 
‘3 i os Var, USugnis *Pseudospatha tanganyicensis 
ji ‘‘ var. servainiana : = - living- 
i = i Var Sturanyd stoniana 
. s callista a 2) ortmannt 
ss elongata * - stappersi — 
: ey giraudr e ie bourguignati 
3 gravida - is subtriangularis 
Some of these 29 forms are quite variable in shape and sculpture, so 
that the specific limits in this group are far from cleared up. Neothauma 
is a true viviparid, on characters of shell and operculum, as well as on soft 
parts and anatomy. It may be regarded as an enlarged edition of Vivi- 
parus, remarkable for its bulk and extreme variability. The curious 
little amnicolid which we have provisionally referred to the Indian genus 
