34 Bulletin American Museum of Natural History [Vol. LIII 
Previously recorded by de Man, from the Lower Congo (near Boma?), the 
River Kole, a tributary of the Lohali (Aruwimi), and from Bima, Uele; by Lenz, 
from the Ituri River at Avakubi, and the Falls of the Bim, a tributary of the Rio 
Benito, Spanish Guinea. 
Avakubi, Ituri River, October 8, 1907, 10%; October 1909, 180. 
(7 immature), 23° (7 ovigerous); October 31, 1909, 4c7 (1 immature); 
November 21, 1909, 207; December 1913, 7 (4 immature), 42 (3 
ovigerous). Batama, September 18, 1909, 1c? (immature), 32. Niapu, 
November 1913, 36 (mostly immature), 119. No locality, 4c (2 
immature) and a carapace; without data, 2c” (1 immature). 
An examination of the splendid series of specimens here referred to 
. this species, comprising 75 males and 41 females, of which ten are oviger- 
ous, convinces me that M. lenzii (de Man) and M. duz var. congoensis 
(de Man) represent but growth stages of the male sex. Of the males, 
just about half have hands of the lenziz type. In each of the lots in 
which they were found, they are smaller and undoubtedly immature 
individuals. Were one to segregate them on the basis of their lenzzz 
characters, there would be left no smaller or younger stages of the adult 
M. duz in the entire collection. Moreover, the female specimens would 
all separate out with the lenziz males, as the relative proportions of the 
joints of their second legs approach that type more than they do the 
typical dux form. In fact, they tend considerably toward the females of 
M. sollaudii (de Man), especially as the carpus is longer than the palm. 
The female of M. dux has been well characterized by de Man (loc. cit., 
1912, p. 31), in spite of his meager material. As he remarks, the stouter 
second legs will always distinguish the females of this species from those 
of M. sollaudi, as will the more ovoid eggs in ovigerous specimens. 
De Man (loc. cit., 1912, p. 13) has already suggested that his M. 
lenzii might be the Gansta male of M. dux, and, as stated above, our 
material certainly seems to indicate that this is so. The larger and 
better developed males are very typical dux, the smaller, less mature 
specimens MM. lenzii, and the variety congoensis but an intermediate 
growth stage between the other two, showing possibly in the case of 
de Man’s only specimen a palm relatively a little more shortened than is 
usually the case. M.dux variety congoensis may be the dimorphic male of 
M. dux, as de Man is inclined to think, but I have not found a single male 
specimen having the pronounced characters of the variety. Some of the 
lenzii forms, however, strongly suggest them, and it might well be that 
it is either an alternative form or else a rather rare developmental stage. 
In a tabular summary below, the measurements of several of the 
specimens examined are given, together with similar data taken from 
