910 PUOCEEDINGS OF THE NATIONAL Ml'SEUM. 



* Cameronia comphiiiata BOURGUIGNAT, Un. et Ir. Tan., 1886, p. 76. Lake Tan- 

 ganyika. 



* Camera nia dromauxi BOUKGUIGNAT, Uu. et Ir. Tan., 1886, p. 84. Lake Tan- 



ganyika. 



* Cameronia yiraudi BOURGUIGNAT, Nat. Prod.j 1885, p. 107. Lake Tanganyika. 



* Cameronia ijmlUmeti BOURGUIGNAT, Un. et Ir. Tan., 1886, p. 72. Lake Tan- 

 ganyika. 



* Cameronia jouberti BOUHGUINAT, Uu. et Ir. Tan., 1886, p. 88. Lake Tan- 



ganyika. 



* Cameronia laviyirina BOUKGUIGNAT, Un. et Ir. Tan., 1886, p. 85. Lake Tan- 

 ganyika. 



* Cameronia locardiana BOUKGUIGNAT, Un. et Ir. Tan., 1886, p. 78. Lake Tan- 

 ganyika. 



* Cameronia marioniana BOUKGUIGNAT, Esp. Ouk., 1885, p. 28. Lake Tanganyika. 



* Cameronia maMlUana BOURGUIGNAT, Un. et Ir. Tan., 1886, p. 86. Lake Tan- 

 ganyika. 



* Cameronia moineti BOURGUIGNAT, Un. et Ir. Tan., 1886, p. 89. Lake Tan- 

 ganyika. 



* Cameronia jjulchella BOURGUIGNAT, Un. ot Ir. Tan., 1886, p. 73. Lake Tan- 



ganyika. 



* Cameronia obtusa BOUKGUIGNAT, Uu. et Ir. Tan., 1886, p. 75. Lake Taugauy ika. 



* Cameronia randebeli BOUKGUIGNAT, Un. et Ir. Tan., 1886, p. 90. Lake Tan- 

 ganyika. 



* Cameronia revoiliaita BOUKGUIGNAT, Moll. Tan., 1885, p. 107. Lake Tanganyika. 



* Cameronia vynckii BOURGUIGNAT, Un. et Ir. Tan., 1886, p. 81. Lake Tan- 

 ganyika. 



Genus MONOCONDYL^EA d'Orbigny, 183S. 

 (Type, Monocondylwa paraguay ana d'Orbiguy. ) 



Aplodon SPIX (not of Rafinesque, 1818), Test. Fluv. Bras., 1827, pi. xxv, figs. 1, 2. 

 Monocondyla'a D'ORBIGNY, Guerin Mag., 1835, p. 37. 

 Spixoconcha PILSBRY, Nautilus, VII, 1893, p. 30. 



Shell rounded to obovate, rather solid, with a low, posterior 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 united; pos- 

 terior indistinct; prismatic layer wide. 



Animal with the marsupium occupying the whole 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 papilla? in front of the branchial opening below; 

 branchial opening large, with numerous small knob-like papillae; anal 

 opening large, without papillae, separated completely from the branchial 

 opening by a bridge; superanal opening not closed below. 



(Group of Monocondylcea guarayana.) 



Shell obovate, inflated, solid, often slightly produced just behind the 

 center of the base; beaks full, turned inward and forward. 



