1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo BEyA 
Kery To ETHIOPIAN FAMILIES OF PELECYPODA 
1. Shell equivalve, wedge-shaped, the hinge without teeth, the beaks terminal at 
the smaller (anterior) end, a septum across them inside; posterior adductor 
muscle very large. Byssiferous. Estuarine mussels........... Dreissenide. 
Beaks not terminal, or if so, the adductor muscle scars are not greatly unequal. .2. 
2. Interio® “pearly ie Bee OS le es Re lw Se ee Oe ee ce 3. 
Interior PoOreelAnOUss< 500 yo. ee ae dies cj eB Ge Ok ae 5. 
38. Irregular, inequivalve, oyster-like; hinge without teeth; living attached to 
shells, stoned: eba..0 61 cane ii vie og ee Etheriide. 
Equivalve; free in the adult’ stages 8 Oye i os 4, 
4. Hinge having lamellar lateral teeth and shorter cardinals (in African species). 
Unionide. 
Hinge various; toothless, with a series of many short teeth, etc., but without 
lamellar laterals, (in Afriesn Species) oo: 5's .cs's os eters tls oe Mutelide. 
5. No lateral teeth; a 7-shaped cardinal in each valve, another tooth below it in 
the right valve; shell subcircular, with very indistinct adductor and pallial 
impressions....... ee GRAM saree bis Babsls. 6 ba Oe eee ee Cyrenoidide. 
Anterior and posterior lateral teeth present, at least in the right valve (though 
often very small in Egeria, where the cardinal teeth are very large);. car- 
dinal teeth present; shell trigonal, oval or orbicular las eee ei et 6. 
6. Two or three moderately to very strong cardinal teeth, diverging from the beaks 
in both valves, on a distinctly or strongly developed hinge-plate.......... re 
Cardinal teeth minute and conspicuously unlike in the two valves, not more than 
two in each valve, the laterals far larger though lamellar; the hinge-plate 
extremely narrow; shell thin, rather small or minute.......... Spheriide. 
7. No pallial sinus in African fresh-water genera...............+..-. Cyrenide. 
A pallial sinus present in African fresh-water genera.............. Donacide. 
TELEODESMACEA 
Cyrenide 
Shell trigonal to oval, moderately or very solid, porcellanous, covered with a 
yellow to olivaceous or brown periostracum ; hinge-plate developed, bearing 2 or 3 
cardinal teeth diverging from the beaks in each valve, and anterior and posterior 
lateral teeth. Ligament external; pallial line entire in the African genera. The 
mantle is free, except posteriorly where a partition divides off a siphonal cavity. 
Siphons quite chert and separate or represented by mere orifices. Gills concrescent 
posteriorly. Labial palpi rather short, triangular. Oviparous so far as known. 
A number of genera in nearly all tropical and subtropical regions 
of both hemispheres. Corbicula, generally spread in East Africa, appears 
to be in course of invading the West African fauna. 
Key to African Genera of Cyrenide 
1. Lateral teeth absent in both valves. Shell thin and fragile. 
Soleilletia Bourguignat. 
Lateral teeth well developed in both valves, long and finely crenulate. Shell 
thick:@nd SOUGe ses hci ees Phd idles 9 o Corbicula Megerle v. Mihlfeld. 
