336 Bulletin American Museum of Natural History [Vol. LIII 
Rissoa subgenus Horea E. A. Smiru, 1889, Ann. Mag. Nat. Hist., (6) EV, 9.175. 
Monotype: Rissoa (Horea) ponsonbyi E. A. Smith. Not Horea Bourguignat, 1888. 
Lechaptoisia ponsonbyi (EK. A. Smith) 
Text Figure 70a-b 
Rissoa (Horea) ponsonby: E. A. Smrru, 1889, Ann. Mag. Nat. Hist., (6) IV, p. 175. 
Lechaptoisia ponsonby: E. A. Smith. Ancry, 1894, Bull. Soc. Zool. France, 
XIX, p. 29; 1901, Journ. de Conchyl., XLIX, p. 224. E. A. Smirn, 1904, Proe. 
Malacol. Soc. London, VI, 2, p. 94. Ancry, 1907, Bull. Scientif. France et Belgique, 
(5) IX, (1906), p. 254. 
Horea ponsonbyi E. A. Smith. G. B. Sowrrsy, 1894, ‘List of Shells of Lake 
Tanganyika,’ p. 2, Pl., fig. 13. E. v. Marrens, 1897, ‘Deutsch Ost Afr., IV, Be- 
schalte Weichth.,’ p. 211. 
Lake Tanganyika: originally described from the eastern shore without more 
definite locality (E. C. Hore Coll.). 
a b 
Fig. 70, a-b, Lechaptoisia ponsonbyi (E. A. Smith). 6.5 and 6.7 mm. long. 
PELECYPODA 
Aquatic mollusks without distinct head and without radula, protected by a 
bivalve shell, the two valves united by an elastic dorsal ligament and usually artic- 
ulated together by hinge-processes or ‘“‘teeth”’; connected also by adductor muscles 
passing from one valve to the other and serving to pull them together. In the fresh- 
water groups there are two (rarely one) pairs of leaf-like gills between mantle and 
foot, serving also as gatherers of food and often as marsupial pouches for the eggs and 
embryos. 
In the Ethiopian Region this class is represented by eight families, 
classified thus!: 
Cyrenidee 
Spheeriidee 
Superfamily Tellinacea: Donacide. 
|Superfamily Lucinacea: Cyrenoidide 
Unionide 
pace Naiadacea < Mutelidse 
Etheriide 
[Superfamily Mytilacea: Dreissenidse 
Superfamily Cyrenacea 
Order Teleodesmacea 
Order Prionodesmacea 
1The arrangement given is that of Dall. In the classification of Pelseneer the first six famili 
placed in the Order Kulamellibranchia, the last one in Filibranchia. — paietiaaiias 
