MOLLUSCA FROM THE SOUTHKEN SUDAN". 259 



Genus PsEUDOMUTELA, Simpson. 

 PSEUDOMUTELA PLICATA, von Martens. ■ 



Mutela plicata, vou Martens, 1866, Malak. Blatt. p. 10. 



A single specimen was taken at Gebel Ahmad Agha. Since only 

 two examples appear to have been recorded previously, this is an 

 interesting find. These are in the British Museum (Nat. Hist.); one is 

 figured by Sowerby in ' Conch. Icon.' vol. xvi. 1868, pi. 2. fig. 3, and both 

 are referred to by Jickeli, p. 270. The locality in the British Museum 

 register is " Cataract at Syene,'' Jickeli gives Sennaar (Kotschy), and 

 Sowerby gives no locality. Gebel Ahmad Agha is about one degree south 

 of the province Sennaar; the town of this name^, however, is on the Blue Nile, 

 lat. 13° 25' N. My specimen measures, long. 87, greatest alt. 31*5, alt. at 

 umbo 23, crass. 17 mm., and is intermediate in size between the two in the 

 British Museum, the largest of which measures, long. 106^ greatest alt. 36, 

 alt. at umbo 27*5, crass. 20 mm. These latter are named Iridina plicata, 

 Parreyss. In the Collection Morelet, ' Voy. Welwitsch,' 1868, p. 40, the 

 species is attributed to Parreyss, but there is no description. Yon Martens 

 (Malak. Blatt. 1866, p. 10) mentions a specimen in the British Museum, and 

 gives a diagnosis: though this is very brief, the species must be credited to 

 him as the first really to describe it. Sowerby in 1868 describes it more 

 fully, calling it Mycetopus plicatiis, and referring it to Gray in MS. 



P. jjlicata somewhat resembles Mutelina rostrata, but is distinguished by 

 being subquadrate posteriorly, and gaping at both ends, by having a rather 

 wide groove running from the umbo to the posterior end, and a larger 

 cardinal tooth in the right valve. The shells in the British Museum are 

 yellowdsh externally, while mine is darker, being greyish green, with the 

 nacre salmon-pink, merging into bluish white at the margin. 



Genus Spatha, Lea. 

 Spatha eubens. Lam. 



Anodonta ruhens, Lamarck, 1819, Hist. Nat. Aiiim. sans A'ert. vol. vi. pt. 1, p. 86. 

 Spatha cailUaudi, von Martens, 1866, Malak. Blatt. vol. xiii. p. 9. 



An adult specimen measuring long. 112, alt. 73, crass. 42 mm., as well 

 as the right valve of a still larger example measuring long. 145, alt. 97 mm., 

 were obtained from a fishing boat at Kosti. Immature shells in different 

 stages of growth were taken at Ad-Duwem, Tawila, and Lake Shambe. 



Von Martens considered this Nile species of Spatha distinct from that 

 described by Lamarck from West Africa, and therefore called it S. cailUaudi. 

 I have, however, compared my specimens from the White Nile, and also 

 some I obtained from a pond at Shabra Maut, near Gizeh, with examples 

 r om West Africa in the British Museum (Nat. Hist.), and I consider them 



