MOLLUSCA OF THE SUDAN 
425 
most convex whorls ; out of one hundred and ten only five, and these 
immature, had a keel on the spire, this was observed on very few 
adults and on one only was it continued on the body whorl (var. 
uniliata , Germain). They were nearly all of a uniform yellowish 
horn-colour, with the exception of nine which had dark brown 
spiral bands, these included the five keeled young shells. At Gebel 
fin about forty individuals were found which were greatly decol¬ 
lated, whereas those at Mogran were only slightly so. The southern 
specimens are less robust and have a smaller spiral angle. Thirty- 
three are spirally striped with dark brown, only eight are self- 
coloured similar to those found near the mouth of the river, and three 
of these have a keel on the whorls of the spire. Fourteen of the 
striped shells have two keels on the spire, which are not continued 
on the body whorl (var. hicarinata). Ten individuals were met with 
at Hillet Abbas, which are also decollated, five are unicolorous, the 
rest have dark stripes. Four have keels on the spire. 
Vivipara unicolor , Olivier, which is equally variable, was found 
at all the stopping places and also near Mogran. Those from the 
latter locality have almost convex whorls with but little trace of 
angularity, whereas one taken at Gebel En, as well as those met 
with at intermediate places, are distinctly biangular (var. biangulata, 
Kust.). Some have in addition several spiral moniliform threads, 
these are especially clearly exhibited on a shell from Hillet Abbas, 
which thus approaches the var. robertsoni , Frauenf. 
I did not find specimens of Corbicula so numerous in the White 
Nile as lower down at Aswan, nevertheless I met with individuals 
characteristic of two of the three groups into which M. Pallary 
divides the species. At Gebel En were found three good specimens 
of the triangular form, G. artini, Pallary, and at Hillet Abbas three 
much worn single adult valves, and two young living examples. 
C. consobrina , Caill., occurred at these two localities as well as near 
Mogran. A single valve taken at Hillet Abbas is the largest, 
measuring 31 mm. in height, and 34 mm. in width. 
Numerous specimens of Sphaerium sp . indet ., were obtained at 
Gebel fin, Hillet Abbas, Fachi Shoya, and Tawila. 
Both an adult and a young example of Nodnlaria (?) parreyssi , 
v.d. Busch, were found at Fachi Shoya. Eight individuals in differ¬ 
ent stages of growth, though none quite mature, were also taken at 
Mogran. At Soba on the Blue Nile there occurred five specimens 
which closely agree with Pallary *s figures of N, mysticus , Bourg. A 
very good example of N, aegyptiaca , Fer., was found at Hillet Abbas, 
and two larger, thinner, and more orbicular specimens were met 
