086 Bulletin American Museum of Natural History [Vol. LIT 
The occurrence of a true medusa or jJelly-fish (Limnocnida tan- 
ganice R. T. Giinther) in Lake Tanganyika, discovered by Bohm in 
1883, for the first time focussed the interest of the scientific world upon 
the lake. The number of fresh-water medusxe then known was very small, 
so that considerable significance was attached to this find. In recent 
years, however, allied forms of Limnocnida have been found in Lake 
Victoria, in various African rivers, such as the Nile, the Zambezi and the 
Limpopo, and in certain streams of India; while other types of fresh- 
water meduse are known from Lake Qurum in Egypt, the Caspian Sea, 
the Yang-tse-Kiang, and some North American rivers.! 
Notwithstanding the considerable amount of work done on the 
fauna of Lake Tanganyika, we are as yet far from being adequately in- 
formed with regard to the distribution in depth of its various inhabitants, 
except, perhaps, in the case of some of the mollusks. It is quite possible 
that some of the true deep-water or bathylimnetic forms are still totally 
unknown. At any rate, it does not appear possible to draw up a list of 
the forms occurring only beyond a depth of 50 meters. It is furthermore 
impossible to state with any degree of certainty whether the bathylim- 
netic fauna is different; at various depths and whether it is the same over 
the entire area covered by the lake. : 
The Mollusca are by far the most interesting part of the Tanganyi- 
kan fauna. Ever since Richard Burton and J. H. Speke upon discovering 
the Lake (February 18, 1858) obtained the first specimens, they have 
aroused the curiosity of biologists and been the subject of much specula- 
tion.? The literature dealing with them has become quite extensive, yet 
they are far from being satisfactorily known. Of the so-called thalassoid 
forms not half of the genera have been e amined anatomically and 
the ecological conditions under which they live have been but very 
superficially studied.’ | 
The molluscan fauna of Lake Tanganyika is extremely abundant in 
species as well as in individuals. According to our present estimate, based 
‘They have also been vaguely reported by Kandt from Lake Kivu and from one of the small 
lakes, Tshohoha, in Ruanda. 
‘The shells collected by Burton and Speke were studied by Woodward, S. P. 1859. ‘On some new 
freshwater shells from Central Africa.’ Proc. Zool. Soc. London, pp. 348-350, Pl. xtvu. The comprised: 
Iridina spekii, Grandidieria burtoni, Spekia zonata, and Edgaria nassa. 
3In the taxonomic part of this Report all mollusks known from Tanganyika were listed with 
full references to published records. With regard to the synonymy of the numerous forms named by 
Bourguignat we have generally accepted the conclusions reached by C. F. Ancey, E. A. Smith, and L. 
peo i as een the isa recent publications: 
TG ay. bo Ne 4. ‘Some remarks on the Mollusca of Lake Tanganyika.’ ; : 
London, Vi 3, See e ganyika.’ Proc. Malacol. Soc. 
neey, C. F. 1907. ‘Réflexions sur la faune malacologique du lac Tanganika et catalogue 
Mollusques de ce lac.’ Bull. Scientif. France et Belgique, (5) Tx, (1906), pp. 259-270. is 
Germain, L. 1908. ‘Mollusques du lac Tanganika et desesenvirons.’ In‘ Rés. Scientif. Voy. Afr. 
Foa.’ (Paris), pp. 612-702. This valuable account contains photographic reproductions of several of 
Bourguignat’s types. 
