CRIST ADENS 1 1 55 



Cristadens borneensis (Issel). 



Shell long rhomboid, rather thin, subcompressed, inequilat- 

 eral ; dorsal and ventral outlines nearly straight and parallel ; 

 anterior end rounded ; dorsal slope obliquely truncate or sub- 

 truncate ; posterior ridge low, rounded, ending near the base 

 in a blunt point : beaks but little elevated, the sculpture con- 

 sisting of numerous, close-set zigzag-radial, subnodulous 

 ridges. This sculpture extends well out over the disk and 

 gradually changes to fine, irregular, concentric sculpture; 

 sculpture on the dorsal slope subplicate ; epidermis yellowish- 

 green or brownish-igreen, often with several wide or narrow 

 green rays on the dorsal slope ; pseudocardinals compressed, 

 ridged, often cut up into dentilations ; laterals delicate, straight, 

 remote ; nacre bluish-white, iridescent. 



Length 48, height 23, diam. 13 mm. 



Borneo ; Siam ; Malacca. 

 Unio plicatulus Lea, Pr. Ac. Mat. Sci. Phila., Ill, 1859, p. 152; 



Jl. Ac. Nat. Sci. Phila., IV, i860, p. 247, pi. xxxvii, fig. 126; 



Obs., YII, i860, p. 65, pi. XXXVII, fig. 126. — Reeve, Conch. 



Icon., XVI, 1865, pi. XXII, fig. 102. 

 Margaron (Unio) plicatulus Lea, Syn., 1870, p. 31. 

 Unio horneensis Issel, Moll. Borneo, 1874, p. 113. 

 Ctenodesma horneensis Simpson, Syn., 1900, p. 853. — Haas, 



Conch. Cab., Unio, 1912, p. 135. 

 Virgus horneensis Haas, Con. Cab., Unio, 1910, pi. xiii, figs. 



4-5- 

 Unio penisatus Fischer and Crosse, Miss. Sci., Pt. 7, II, 1894, 



p. 590. 



Three specimens of the above are before me, none of which 

 are quite so large as the type, which is not in the Lea collec- 

 tion. Two of these shells are more rounded behind than the 

 type ; in all of them the epidermis is somewhat wrinkled. Two 

 have bright green posterior rays ; the other is rayless. 



Lea's name was preoccupied by Kuster, or Charpentier. for 

 a Mexican species in 1856. The name proposed by Issel in 

 1874 will have to be used. 



The name penisatus was proposed by Fischer and Crosse, 

 because Lea's name plicatulus was preoccupied by Kuster. 



