42 DR. J. G. DE MAN ON A NEW [Jan. 20, 
figured (A. Milne-Edwards, ‘ Observations sur les Crabes des 
eaux douces de l'Afrique,’ Paris, 1887, p. 4, pl. 2. fig. 8). I 
therefore propose the name of Potamon latidactylum for this new 
species that inhabits Liberia and Ashanti, on account of the 
characteristic shape of the hands, and as this feature was not alluded 
to in my somewhat incomplete description of 1881, another will, 
I think, be welcome. 
The rivers of West Africa and of the Soudan are inhabited by 
several species of Potamon which differ from the other species 
of this subgenus in the existence of éwo epibranchial teeth behind 
the external orbital angle, instead of one as is usual. I was 
at first inclined to create for these species a new subgenus, but 
the differences from Parathelphusa are, indeed, of too little 
importance. These species are the following :— 
Potamon aubryt H. M.-K. Gaboon. 
» pelit Herklots. Gold Coast. 
BP africanum A. M.-K. Gaboon ; French Congo. 
a decazet A. M.-K. French Congo. 
43 emarginatum Kingsley. West Africa. 
» floweride M. Soudan. 
35 latidactylum, n. sp. Upper Guinea. 
It must, however, be observed that P. emarginatwm is con- 
sidered by Miss Rathbun (Proc. U.S. National Museum, xxii. 
1900, p. 285) to be the same as P. aubryi. P. latidactylum 
may at first sight be distinguished from P. africanum by the 
different shape of the eaxtraorbital and epibranchial teeth and by 
the different form of the hands, especially of the fingers, but there 
are still other differences. 
The cephalothorax is a little more enlarged than in the species 
from the ‘“Ogoué,” as is readily shown by the measurements. 
The upper surface is somewhat less depressed, the branchial regions 
are somewhat swollen, especially the anterior ones, and the gastric 
and cardiac areas are, in aged individuals, also slightly convex and 
not so much depressed as in P. africanum. The oblique furrows 
or depressions limiting off the protogastric areas from the anterior 
branchial lobes are scarcely distinguishable in P. africanwm ; in 
the other species, however, they are quite distinct, and, in adult 
individuals, rather deep. The urogastric lobes and the cardiac 
area are a little broader in proportion to the breadth of the 
carapace than in P. africanum. In the latter the gastric region 
is faintly granular or rugose just behind the postfrontal ridge, 
but in the new species it appears everywhere smooth, though 
finely and sparsely punctate. The anterior branchial area is 
slightly rugose in P. africanum, but not marked with oblique 
wrinkles ; these are quite distinct in the species from the River 
Prah and Liberia ; on the posterior branchial lobe these rugosities 
occur in both species, they are, however, thinner and finer in 
P. latidactylum. The posterior part of the upper surface 
