MOLLUSCA FROM THE SOUTHERN SUDAN. 253 



Unio sennaariensis, Kiister (fig. 6), is also probably an immature form ot 

 this species. Herr Boettger regards it as a variety and records a single 

 specimen from Gebel Ahmed Aghii. 



Some of the shells have the dorsal margin lower posteriorly than U. eurys- 

 selliniis, and come nearer to the type in form. These generally have the 

 nacre either white or tinged with salmon-pink within the umbo. 



It would be unwise to found new varieties on any of these shells since 

 neither Bourguignat^s nor mine are quite rnature. 



The largest specimen I got at Manshiya measures, long. 54, alt. 31, crass. 

 24 mm. Herr Hagg states that the Swedish Expedition obtained twenty 

 specimens, of which the dimensions exceed any that I have found in either 

 district, having long. 73-5, alt. 42^ crass. 32 mm. 



The holotype is from Joseph's Canal, Lower Egypt. The species is reported 

 from Upper Egypt, also previously from the White Nile, and Mr. A. E. Smith 

 has recorded it from Lake Tanganyika. 



NODULARIA (OiELATURA) ^GYPTIACA, Ccdlliaud. 



Unio cegyiJtiacus, Oailliaud, 1823, 'Voy. a Meroe,' vol. ii. pi. 61. fios. 6, 7 ; 1827, vol. iv. 

 p. 263. 



I found this species less numerous but more widely distributed than 

 N. nilotica. Sixteen specimens were taken, none are mature ; the shell 

 structure is thin, externally brownish green in colour^ the nacre is pinkish 

 purple, in some examples the pink tone predominates and in others the blue. 

 No wrinkles (" flabellations '^) observed. 



The largest specimen was found at Mogran ; it measures, long. 40, greatest 

 alt. 28, crass. 16 mm. Others occurred at Ad-Duwera, Tawila, Kosti, Hillet 

 Abbas, Masran Island, south of Melut, Waw, Taufikiya, and Lake Shambe. 



This species has been reported from Upper and Lower Egypt, in which 

 district I have also taken examples, the Upper Nile basin, and Central Africa. 



Var. SHAMBiENSis, var. no v. (PI. 18. figs. 4-7.) 



Diagnosis. — More oval in contour than the type, more swollen, dorsal 

 margin more curved. Exterior brown, the nacre varies from pink to purple, 

 in two it is rose-pink merging into salmon-pink within the umbo, while in 

 another it is bluish- white with sahnon-pink within the umbo. Some of the 

 examples are remarkably solid, and when this is the case the lamellar anterior 

 teeth of the right valve become greatly thickened, divided, and jagged. 



This is a very distinct form having the muscle-scars and the teeth, when 

 the test is thin, of N. cegijptiaca, while the shape is something like N. nilotica, 

 but none of the specimens has the wrinkles of that species. The higher 

 posterior rostrum distinguishes it from N. parretjssi, though the teeth when 

 the test is thick resemble those of that species. 



