NO. 1205. SYNOPSIS OF THE NAIADES SIMPSON. 835 



narrow in front; palpi enormously long, apparently slender, pointed 

 behind, where they project free for some distance; mantle thin, with a 

 wide, slightly thickened border, faintly papillose behind, there seeming 

 to be but little distinction between anal and branchial openings; anal 

 opening apparently smooth. 



Section STJBORBICtTLUS Simpson, 1900. 

 (Type, Monocondylun orbiciiJaris Morelet.) 



Shell compressed, nearly round in outline, feebly biangulate, and hav- 

 ing a posterior dorsal wing; beaks low; hinge with a single, com- 

 pressed, smooth, slightly curved, triangular tooth in each valve. 



PSEUDODON ORBICULARIS Morelet. 



* Monocondylus orbicularis MORELET, Rev. et Mag., XVIII, 1866, p. 167. 



* Pseitdodon orbicularis MOKELKT, Ser. Conch., IV, 1875, p. 338, pi. xvi, fig. 5. 



* Monocondyla-a orbicularis P.ETEL, Couch. Sam., Ill, 1890, p. 174. 



Siam; Cambodia. 



Section TB.IGONODON Conrad, 1865. 



Shell solid, compressed, rhomboid, round in front, widely and faintly 

 biangulate and rough behind; surface irregularly concentrically wavy 

 sulcate; hinge with a strong triangular pseudocardinal in the right 

 valve, having a decided excavation behind it, and at the posterior side 

 of the pit a faint tootli ; there is one strong triangular tooth in the left 

 valve and a vestige of one in front of it at the upper edge of the shell; 

 anterior scars irregular; dorsal scars crowded close to the hinge line. 



(Type, Mouocondylfe'a crebristriata Anthony.) 

 t PSEUDODON CREBRISTRIATUS Anthony. 



* Monocondylcm crebristriata ANTHONY, Am. Jl. Couch., I, 1865, p. 205, pi. xvm, 



fig. 1.* P.ETEL, Conch. Sam., Ill, 1890, p. 174. 



* Trigonodon crebristriata CONRAD, Am. .11. Conch., I, 1865, p. 233. 



* Maryaron (Monocondylwa) crebristriata LEA, Syn., 1870, p. 72. 



* Unio crebristrialus SOWERBY, Conch. Icon., XVI, 1868, pi. xcv, fig. 517. 



" Pseudodon crebristriatum HANLEY and THEOBALD, Conch. Ind., 1876, p. 5, pi. ix, 

 fig. 3. 



* Unio rondembuschii SOWERBY, Conch. Icon., XVI, 1868, pi. xcv, fig. 518. 



t PSEUDODON CREBRISTRIATUS var. PEGUENSIS Anthony.' 



* Monocondyla-a peguensis ANTHONY, Am. Jl. Conch., I, 1865, p. 205, pi. xvm, fig. 



2. *P,TEL, Conch. Sam., Ill, 1890, p. 174. 



* Mar gar on (Monocondyla>a) peguensis LEA, Syn., 1870, p. 73. 



* Pseudodon crebristriatum var. peguensis HANLEY and THEOBALD, Conch. Intl., 



1876, p. 5, pi. ix, fig. 5. 



Burma; Pegu; Cambodia! 



'Typically quite different from P. crebristriatus, hut our large series seems to show 

 an almost complete connection. 



