NO. 1205. SYNOPSIS OF THE NATADES— SIMPSON. 861 



high, down-carved posterior ridge ruus to the posterior basal point, and 

 between this point and the posterior point of the wing the outline is 

 deeply incurved; base and lower part of anterior end rounded; surface 

 slightly sculptured with concentric ridges; beak sculpture probably 

 zigzag rayed; anterior tooth of left valve elongate, slightly corru- 

 gated, that of the right double; laterals in left valve double, single 

 in the right, straight, elongated, thin, and prominent; nacre, rose 

 tinted. 



Animal unknown. 



PSEUDAVICULA JOHNSTONI Smith. 



Unio {metaptero.) jolinstoni Smith, Pr. Zool. Soo. Loud., 1893, p. 640, pi. lix, figs. 

 18-20.' 



Lake Mweru, British Central Africa. 



Genus ARCIDOPSIS Simpson, 1900. 

 (Type, Vnio footei Theobald.) 



Shell inequilateral, elongated, with dorsal and ventral lines nearly 

 straight and parallel; anterior end strongly and obliquely truncated 

 from the beaks to the anterior base, and ending in a rather sharp but 

 rounded point below; posterior end obliquely truncated above, rounded 

 below; posterior ridge full, rounded; the shell in front and below rather 

 compressed; surface concentrically and radially ridged; pseudocardi- 

 nals strong, two in the right valve, one in the left, and supported by a 

 strong, cardinal rib; muscle scars well impressed; parallel line dis- 

 tinct. Animal unknown.'- 



ARCIDOPSIS FOOTEI Theobald. 



" Unio footei Theobald, Jl. As. Soc. Beng., XLV, 1876, p. 187, pi. xiv, figs, 9, 9a. 



Kistna Eiver, India, 



The following are indeterminate Oriental Unionidse : 



Unio acrorrhynchus von Martens, S. B. Nat Ft., 1894, p. 214, Korea. 



Unio alfierianus Bourguigxat, Voy. Choa, 1885, p, 43, Choa, Central Africa. 



Unio antiniloticus Bourguigxat, Bull, Soc. Zool. Fr., XI, 1880, p. 482, pi. xii, fig. 5. 



High Senegal. 

 Unio ascia Haxley, Bir. Shells, 1856, p. 385. 



Unio hridonxi Bourguigxat, Uu. & Ir. Tan., 1886, p, 13. Lake Tanganyika. 

 Unio cyamus Philippi, Zeits flir Mai., A'^III, 1852, p. 125. S. Africa. 

 Unio diespitei- Mabille, Bull. Soc. Mai. Fr., IV, 1887, p. 162. Tonkin. 

 Uiiio dolichorhynchus Tapperoxe Canefri, Ann. Mus. Civ. Gen., 1889, p. 348. 



Mercato de Mandelay. 



' A remarkable Naiad, closely imitating some of the South American Prisodons in 

 general appearance, to which it may be nearly allied. 



2 Unfortunately Theobald's Latin description of Unio footei is not at all complete. 

 No laterals are mentioned, and he says nothing of the color of the epidermis or of 

 the nacre. The beaks were too much worn in his specimens to give auy characters. 

 The shell resembles some of the Areas of the Barhatia group, and may not belong to 

 the Unionidw at all. 



