MOLLTJSCA FROM THE SOUTHEEN SUDAN. 261 



Ad-Duwem. None are mature. They agree with the figures of both Krauss 

 and Jickeli, but are not so large. I compared them with two specimens in 

 the British Museum (Nat. Hist.) found in the White Nile by Captain Flower, 

 and also with some from Natal. They are similar in shape and muscular 

 markings to all of these, but are not so large as the former; m}^ largest, 

 however, is nearly the same size as the smallest from Natal. They differ in 

 the colour of the nacre^ mine being bluish or greenish white, and the others 

 pink. Krauss says the inner surface of his shell is white, the middle flesh- 

 colour, while the margin is green and reddish iridescent. Much stress cannot 

 be laid on the tint of the nacre, as it is known to vary greatly in manv 

 freshwater bivalves. 



My largest example from Mogran measures, long, 68*5, alt. 84, crass. 

 18"5 mm. Krauss's specimen measures, long. 113, alt. 52 mm. Flower's 

 specimen measures, long. 112, alt. 55 mm. The largest from Natal measures, 

 long. 70, alt, 37 mm. 



It is interesting to note what a wide range this species has. The type of 

 S. v:a]ilher<ji is from the Apies River, the most southern source of the 

 Limpopo lliver. The species has been reported from several other localities 

 in South, East, Central, and West Africa ; amongst them may be mentioned 

 Khartum, Sennaar, between Ad-Duwem and Goz Abu-Groma (Hdgg), Bahr 

 el-Zarafa (JRolil), and Lake Tchad. 



Spatha maexoi, Jickeli. 



Spatha marjioi, Jickeli, 1874, 'Fauna N.O.-Afrikas,' p. 264, pi. 8. lig. 3. 



The right valve of a specimen of this species was found on Abba Island 

 opposite Fachi Shoya. It measures, long. 106, alt. 52 mm. Two smaller 

 dead and worn examples were taken in recently dredged mud a short 

 distance up the Bahr el-Zarafa. This latter locality is the habitat of the 

 holotype, whose long, equals 85, alt. 40*75 mm. 



Spatha fourtaui, Pallanj, 



Spathella fourtaui, Pallary, 1902, Bull. Inst. Egypt, ser. iv. no. 3, p. 96, pi. 1. fig. 3. 



Twenty-seven specimens were taken at the following localities : Tawila, 

 Masran Island, near Gebel Ahmad Agha, south of Melut, Taufikiya, Hillet 

 al-Nuwer, and fragments of a fair-sized specimen at the southern entrance 

 to the Bahr el-Zarafa. They were most abundant to the south of Melut, 

 where nineteen examples were found. The largest is from Hillet al-Ntiwer ; 

 it measures, long. 63, alt. 29*5, crass. 17 mm. ; it is slightly lower than usual. 

 A single valve from Melut measures, long. 60, alt. 29 mm. 



This species greatly resembles S. marnoi and may possibly be a variety of 

 that species. It shows a certain amount of variation, and some specimens are 

 very like the small examples of S. marnoi from the Bahr el-Zarafa in form 



