1384 MONOCONDYL.^;A 



Cameroiiia Nilclidla BonRGUiCNAT, Un. and Ir., 1886, p. yT,. 

 Cameroiiia obfiisa Bourguignat, Un. and Tr.. 1886, p. 75. 

 Camcrouio randabeli Bourguignat, Un. and Ir., 1886. p. 90. 

 Coiiicroiiia rez^oiliana Bourguignat, i\Ioll. Tan., 1885, p. 107. 

 All from Lake Tanganyika. 



Genus MONOCONDYL^iA d'Orbigny, 1835. 



Aplodon Spix (not of Rafinesque, 1818), Test. FIuv. Bras., 



1827, pi. XXV, figs. I, 2. 

 MonocondyJcea d'ORBJGNv, Guerin Mag.. 1835, p. 37. 

 Spixoconcha Pilsbry, Naut., YII, 1893, p. 30. 



Shell rounded to obovate, rather solid, with a low, poste- 

 rior ridge, which is generally bordered by two or more dark, 

 radiating bands ; epidermis dull olive-green to olive-brown, 

 cloth-like ; hinge with two irregular teeth under the beak in 

 the left valve, and two in the right, the posterior under the 

 beak, the anterior in front of it and interlocking with those of 

 the left valve, the whole generally more or less tuberculate ; 

 nacre soft, silvery, with iridescent shades ; anterior scars unit- 

 ed ; posterior indistinct ; prismatic layer wide. 



Animal with the marsupium occupying the w hole length of 

 the inner branchiae : gills very large, curved below, inner very 

 much the larger, united the whole length of the abdominal sac ; 

 palpi small, round below, attached along their upper edge; 

 mantle thick, greatly thickened at the edge, with a few papillae 

 in front of the branchial opening below : branchial openings 

 large, \\ith numerous small knob-lik-e papillae; anal opening 

 large, vyithout papilUe, separated completely from the bran- 

 chial opening by a bridge ; superanal opening not closed below. 



Type, Monocondyhva para (!;iiay ana d'Orbigny. 



In Monocondyhca the teeth are imperfect, there being us- 

 ually a single rounded tooth in the left valve often with a pit 

 behind it and one tooth in the right valve, or frequently there 

 is a smaller one in front of it with pit between. In M. reticu- 

 lata the teeth are very irregular and somewhat broken up into 

 denticles. 



