1927] ' Pulsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo “ots 
Littoridina) inhabit both brackish and fresh water; but most of the 
genera are confined to fresh water. The family is closely related to the 
marine group Rissoide. 
_ Nearly all the genera are oviparous, depositing the eggs in chitinous 
capsules, which adhere strongly to shells, stones, and like objects. The 
New Zealand and American species of Potamopyrgus are viviparous, but 
whether this is also true = the African form referred to that genus, 
is unknown. 
Two subfamilies, Bulimine and Amnicoline, are represented in the 
Ethiopian Region. 
Buliminee 
Operculum solid, mainly calcareous, largely concentric, lodging at the edge of the . 
peristome. Shell ovate-conic, rather thin, the peristome continuous. 
Sides of the foot smooth, continuous. A right cervical, epipodial lobe serves as a 
water conduit. The central tooth of the radula has basal denticles. 
This subfamily comprises all known genera having the operculum 
calcareous. It occurs on all the continents of the Old World and one 
European species has been introduced locally in America. } 
Authors are conspicuously at variance as to the number of genera of 
Bulimine and their limits. The type species of Bulimus (Bithynia 
Leach) is known to have a concentric operculum with a small spiral 
nucleus, but this nuclear character is often overlooked, being visible 
only in young or quite unworn examples. In Gabbia Tryon and Digyr- 
cidum Locard the spiral portion is larger, but the shell and soft parts are 
not otherwise different so far as known. Annandale and Prashad! sepa- 
rate Hydrobioides Nevill and Paranerita Annandale as genera on account 
of the thickened peristome; Digoniostoma Annandale on the same ground, 
and because of the basally angular peristome. All of these appear to 
have the operculum initially spiral, later concentric, with an inner cal- 
careous layer. When these groups are better known, further distinctive 
characters may be found in the penes or other organs, but for the present 
we are disposed to rank all as subgenera of Bulimus. 
Mysorella Godwin-Austen, which has an operculum of the ordinary 
bulimine type, differs by its dentition. 
Alocinma Annandale and Prashad? is certainly not related to Amni- 
cola. The operculum is thick and calcareous, too large for retraction into 
the shell, characters of Bulimus; in Amnicola it is thin and corneous, 
retracting well into the shell. Though mainly spiral, the operculum of 
1 had, 1921, Rec. Indian Mus., XXII, p. 4 
Hone Fpl ost XVIII, 4 1, p. 28. Type: Amnicola sistanica Annandale and Prashad. 
Seistan, eastern Persia. 
