1927] Pilsbry-Bequaert, The, Aquatic Mollusks of the Belgian Congo 301 
sculpture evolution; few, such as Limnotrochus, have characteristics 
of old age. 
These conclusions are substantially those reached by Boulenger 
respecting the fishes, and by Calman in dealing with the macrurous 
Crustacea; also by Cunnington in his excellent résumé of the Tanganyi- 
kan fauna and flora.1_ They give no support to the hypothesis that the 
Tanganyikan fauna is directly traceable to the marine inhabitants of an 
arm of the Jurassic sea. 
Key to the Genera of Tanganyikan Melaniids 
Many Tanganyikan shells have been collected without the opercu- 
Jum or soft parts. We have therefore framed the following key from the 
shells alone, as more widely useful than one employing characters more 
fundamental. : 
1. Shellsmoother nearly soo a eee ie Re sr ean ar a eae ae 2. 
Shell very distinctly or wtronely sculptured.) ee 5- 
2. Shell semiglobose or oval, dark colored, with a very short spire. Aperture large 
and very oblique; a broad, concave columellar area bounded by a sharp 
ridge on the base giving it a circular appearance...... Spekia Bourguignat. 
Without the above-mentioned characters 0025) 6c 56 hace ee ee ee 3. 
3. Spire very short; surface marked with fine, dark spiral lines...... Re ios 4. 
Spite producer ean: oye ee .Baizea Bourguignat. 
Reymondia Bourguignat. 
Bridouxia Bourguignat. 
4. Shell oval; neritinoid; inner lip covered with a very heavy callus, spreading 
forward Amt Banste sg ooh sho Gia Cie Stanleya Bourguignat. 
Inner lip thickened, but without a forwardly spreading adnate callus; often 
rimate. OF di bilieate ve Se eid tee Tanganyicia Crosse. 
5. Rather capacious, large shells, with the shoulder angular and bearing sub- 
horizontal, radiating spines. . ae Li Ghee aia Cin 
Solid, umbilicate or perforate shail ‘of brochiiaran’ or Upabinats oar not shoals 
speel Nearly circular aperture with continuous peristome. Sadhoture of 
granose spirals HPOUe ROME ali eR a ts 
Imperforate, more or less lengthened, with spiral sculpture and oval or ovate 
DPOVL UG ee as a de GU RIAN ens, eos rh ogee a Cer 8. 
6. Imperforate, top-shaped, the spire short. Last whorl and aperture tapering 
downward toa channelled beak. eee eee. Tiphobia E. A. Smith. 
Umbilicate, the spire rather long, the aperture rounded basally. 
Bathanalia J. E. 8S. Moore. 
7. Shell higher than wide, turbinate, perforate...... Limnotrochus E. A. Smith. 
Shell wider than high, trochiform with flat base, umbilicate. 
Chytra J. E. 8. Moore. 
iW. A. Cunnington, 1920, Proc. Zool. Soc. London, p. 603. 
