252 MRS. JANE LONGSTAFF ON NON-MAEINE 



Family Untonid^. 



Genus Nodularia^ Conrad. 



Section Cselatura, Conrad. 



NODULARIA (CeLATURA) NILOTICA, Caill. 



Unio niloticus, Oailliaud, 1823, 'Voyage a Meroe,' vol. ii. pi. 61. figs. 8, 9; vol. iv. p. 263. 

 ? Unio sennaariensis, Kiister, 1862, ' Conch.-Cab.' p. 280, pi. 94. fig. 6. 



Abundant in the lower part o£ the Bahr al-Abyad, where I found a hundred 

 and forty-two specimens ; the greater number occurred at Mogran and 

 Ad-Duwem, only four were taken on Abba Island and one at Kosti. All are 

 small, and few, if any, mature, but some have such a remarkably thick test 

 that it is possible they may be a dwarf form which never attains full 

 dimensions. 



M. Pallary lays great stress both on the colour of the nacre, and the 

 presence of wrinkles (flabellations) as characters essentially separating the 

 species A^. nilotica and N. cef^i/ptiaca from one another. I have, however, 

 found the colour too variable to be a distinction of specific value. 



Sixty-six of the specimens I took have the nacre salmon-pink, twenty-six 

 purplish-pink, and fifty white. 



The absence of wrinkles is possibly more constant, for I have not observed 

 them on any of the White Nile examples of A. a^ayptiaca, nor on those I 

 found in ponds near the Pyramids of Gizeh. They are generally present on 

 N. nilotica, sometimes on both ends, at other times on one end only, or they 

 may be absent altogether. 



I obtained fair-sized specimens of JS\ nilotica at Manshiya, near Mena, 

 fourteen in number, ten with purplish-pink nacre and four white. 



I also got twelve examples from the same locality of a form which 

 M. Pallary has figured as W. gaillardoti, Bourguignat MS. They appear 

 to me more worthy of ranking- as a variety than a distinct species, for there 

 are shells intermediate in character which it is very difficult to place. With 

 one exception these have all purplish-pink nacre. I also obtained two 

 remarkably short specimens. M. Pallary has suggested that N. gaillardoti 

 may be an intermediate form between N. nilotica and N. parrei/ssi. 



The examples of A^. nilotica from the White Nile show a certain amount of 

 variation. M. Pallary informs me that two have received distinctive names 

 from Bourguignat : one which occurred at Ad-Duwem was called Unio euri/s- 

 seUitms, and M. Pallary has figured it (Bull. Inst. Egypt, ser. iv. no. 3, 

 p. 94, pi. 2. fig. 4). The other, a swollen, sub-quadrate form, was named 

 U. pldhsicus or emeritus in lit. I found it both at Mogran and Ad-Duw6m ; 

 an example from Mogran measures long. 37, alt. 24, crass. 16*5 mm. One 

 of the former measures, long. 36, alt. 23, crass. 14*5 mm. 



