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 StrBORBICTJLTJS Simpson, 1900. 

 (Type, Monocoiidylus orbicularis 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. 



* Monocondijlus oriicularis Morelkt, Rev. et Mag., XVIII, 1866, p. 167. 



* Pseuclodon orhicuJaris Mokelet, Ser. Conch., IV, 1875, p. 338, pi. xvi, fig. 5. 

 ^ Monocondyhea orbicularis P.etel, Couch. Sam., Ill, 1890, p. 174. 



Siam; Cambodia. 



Section TRIGONODON 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 tooth ; 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, Monocondylcca crebristriata Anthony.) 

 t PSEUDODON CREBRISTRIATUS Anthony. 



* Monocondykm creljrisiriata Anthony, Am. Jl. Conch., I, 1865, p. 205, pi. xviii, 



fig. 1.—** PyETEL, Conch. Sam., Ill, 1890, p. 174. 



* Trigonodon crebristriata Conrad, Am.Jl. Conch,, I, 1865, p. 233. 

 "^ Mar gar on (Monocondyla'a) crebristriata Lea, Syu., 1870, -p. 72. 



* Unio crebristriatus Sowerby, Conch. Icon., XVI, 1868, pi. xcv, fig. 517. 



'" Pseudodon crebristriatum Hanley and Theobald, Conch. lud., 1876, p. 5, pi. ix, 

 fig. 3. 



* Unio vondembuschii Sowerby, Conch. Icon., XVI, 1868, pi. xcv, fig. 518. 



t PSEUDODON CREBRISTRIATUS var. PEGUENSIS Anthony.' 



* Monocondylwa peguensis Anthony, Am. Jl. Conch., I, 1865, p. 20.5, pi. xviii, fig. 

 2.— *P^tel, Conch. Sam., Ill, 1890, p. 174. 



* Margaron {Monocondyloia) peguensis l^^A, Syn., 1870, p. 73. 



r" Pseudodon crebristriatum var. peguensis Hanley and Theobald, Conch. Ind., 

 1876, p. 5, pi. IX, fig. 5. 



Burma; Pegu; Cambodia 1 



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

 an almost complete connection. 



