1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 115 
slender and circular in section, acute. The blood is red. The radula has a bicuspid 
central tooth; the laterals are tricuspid and the marginals serrulate. 
This family differs from the Lymnzide in the sinistral organization, 
the slender, subulate tentacles, the bicuspid central teeth of the radula, 
the development of a secondary branchia or ‘‘pseudobranch,” and 
also in details of kidney and genitalia. The shape of the foot and the 
very different teeth of the radula, as well as the red blood and other 
features separate Planorbide from Physidee. 
They avoid the larger and swifter streams. In the forest region 
they occasionally are found in muddy ponds among decaying humus. 
In the savanna country they prefer pools of stagnant water that are 
densely filled with aquatic plants and alge, being then found usually in 
company with Lymnxa. They are oviparous and, at least in the case of 
the Bulinine, the egg-masses are often attached to shells of ee snails 
of the same species. 
This family of water snails has acquired Guo practical 
importance, from a medical point of view, through the discovery that 
many of them are intermediate hosts of certain fluke diseases, especially 
of bilharziosis (See p. 92). 
Planorbine 
Shell flat, coiled in a plane or disk; sometimes more or less ovate and Physa- 
like when young. 
Pranogsis QO. F. Miiller 
Planorbis O. F. Mtuuer, 1774, ‘Verm. Terr. Fluv. Hist.,’ I, p. 152. Genotype: 
Helix cornea Linneus=Planorbis purpura O. F. Muller, as designated by Denys de 
Montfort, 1810. 
Coretus “Adanson”’ J. E. Gray, 1847, Proc. Zodl. Soc. London, p. 180. As an 
equivalent of Planorbis Miller with Helix cornea Linneus as type. This is apparently 
the first use of Adanson’s Coretus in binomial nomenclature and, since its type was 
correctly designated by Gray (by monotypy), it must become a synonym of Planorbis, 
proper, notwithstanding the fact that Adanson’s Coretus was based upon a species of 
Gyraulus. 
Planorbia J. E. 8. Moors, 1901, ‘To the Mountains of the Moon,’ p. 260. Mono- 
type: Planorbia albertensis J. E. 8. Moore. 
Biomphalaria Preston, 1910, Ann. Mag. Nat. Hist., (8) VI, p. 585. Monotype: 
Biomphalaria smitht Preston. 
The shell is usually discoidal, the whorls coiled nearly or quite in a plane, visible 
on both sides, or the last whorl deviating obliquely toward the left. Cavity of the 
whorls not obstructed by teeth or lamine. Right margin of the aperture advancing 
beyond the left. 
The shell of Planorbis has been regarded as sinistral by some authors, 
dextral by others. The unpaired organs show the animal to be sinistral, 
