258 MRS. JANE LOKGSTAFF ON NOX-MARINE 



M. nilotica in having less difference between the height o£ the anterior and 

 posterior ends, the posterior dorsal margin being less produced, the posterior 

 ridge is also very distinct. The mature specimens from Gebel Ahmad Agha, 

 on the other hand, have the posterior dorsal margin greatly produced, and the 

 valves are very veutricose, so that the posterior ridge is not so sharp; also 

 the A'entral margin is more sinuated. Several individuals show faint taxodont 

 teeth on the hinge. The exterior is dull green, the nacre greyish pink. 



An individual from Mogi'an measures, long. 110, alt. at umbo 41, alt. post. 

 50, crass. 210 mm. 



The largest, taken a little north of Gebel Ahmad Agha, measures, long. 130, 

 alt. at umbo -44, alt. post. 56, crass. 36 mm. 



This form was first described by Sowerby in Reeve, but it had previously 

 been figured by Savigny, and was referred to Iridina nilotica, Fer. MS. by 

 Audouin, who wrote the explanation of Savigny's plates. Sowerby names 

 fig. 4 on PI. 2. op. cit. I. nilotica, but it is really the same form as fig. 5, 

 which he calls angustata, differing only in age. It appears more advisable 

 to regard M. aivjiistata as a variety of M. nilotica rather than a distinct 

 species, the chief dift'erenee being a greater expansion of the posterior dorsal 

 margin in the former. 



Sowerby merely gives " Africa ?'' as locality. There are specimens in 

 the British Museum (Nat. Hist.) marked '' Egypt and Senegal," also " Eiver 

 Nile." 



It is reported from Egypt, the Blue Nile, Lake Tchad, and West Africa. 



Genus MuTELlNA, Bounjuiijnat. 



MUTELINA R08TEATA, RanCf. 



Iridina rostrata, Eaiig, 1835, 'Nouv. Arcliiv. Museum,' p. 316. 



Eighty-three specimens were taken at the following places : near Mogran 

 (thirty-five), Ad-Duwem (eighteen), Tawila (five), south of Melut (six), and 

 at Lake Shambe (nineteen). 



The largest were met with at the latter place, and five of the shells found 

 there have the posterior dorsal margin rather higher than usual. The biggest 

 measures, alt. 35, long. 100 mm. 



Many of the younger shells have the epidermis of a beautiful iridescent 

 green colour. 



This species was found by Captain Flower south of Abu Zeit on the White 

 Nile, but it is not recorded from this region by M. Pallary, Herr Hagg, or 

 Herren Boettger and Haas. It occurs in Egypt, and has been reported from 

 Lake Tchad {Germain), as well as from Senegal [Jousseaume). 



