592 Bulletin American Museum of Natural History (Vol. LITT 
gastropods claimed by J. E. 8. Moore, return time and again to their 
thalassoid appearance. It is true that a few genera, such as Spekza, 
Tanganyicia, Lavigeria, Limnotrochus, the Syrnolopside, etc., recall 
various marine shells by their form or sculpture or solidity; but the 
marine appearance is most convincing to those who are relatively un- 
familiar with marine mollusks, and in no case has actual relationship 
with the particular marine shells imitated been demonstrated. ‘These 
mollusks are in no way comparable to the Polyzoa Victorella and Arach- 
noidia or the fresh-water meduse of Tanganyika, which are directly re- 
lated to marine stocks and which, together with some of the algze, alone 
merit Moore’s term “‘halolimnic.”’ To class the so-called ‘“thalassoid”’ 
gastropods with these “halolimnic” organisms muddles the whole 
inquiry. In the mollusks we have to do with cases of adaptive converg- 
ence, such as Spckia, which mimics petricolous Littorinide; or with 
mature stages of sculptural evolution, as in Tzphobia, Paramelania, 
and others, where the convergence to marine shells is merely adventi- 
tious. In these forms the evolution of sculpture based upon axial ribs 
and spiral cords, such as many melanians have, parallels or converges 
toward that of some marine snails having the same fundamental sculp- 
tural elements. In either case, details of sculpture have absolutely no 
phylogenetic significance outside of the limits of each narrow group. The 
solidity of many Tanganyikan Melaniide may be adaptiveinthe case of 
littoral forms; but many melanians elsewhere, such as Paludomus and its 
allies, are equally solid. 
While we thus disbelieve all phylogenetic relationships between the 
thalassoid gastropods of Tanganyika and marine snails, past or present, 
yet we are unable to agree with Germain that the melanians of the lake 
are not fundamentally different from those that inhabit Lake Moero, 
Lake Nyasa, and the Upper Congo basin.!. Nor could we subscribe to his 
statement that the fauna of the upper and mid-Congo ‘‘shows a whole 
series of melanians of marine appearance.’”’ These Congo melanians are 
mostly of small size, usually covered with a thick periostracum, and 
frequently corroded or decollate. They are not in our opinion more 
heavily sculptured nor more solid than many members of the same family 
from the fresh waters of other parts of the world. We fail to find any- 
thing in the fauna of the Congo and its affluents that could be regarded 
11914, [X® Congr. Internat. Zool. Monaco (1913), pp. 563-565. 
