196 ZOOLOGISCHE MEDEDEELINGEN — DEEL III. 
terior rrargin of the carapace is equal to the breadth of the front (at 
least in the co’); in de Man’s specimens the posterior margin is 
broader, especially in the Q. 
As regards 1° en 2° the 4 adult specimens of the ,,Siboga’’-expedition 
and the not yet full-grown Museum specimen (¢') of Nias (the very loca- 
lity whence one of Nobili’s examples originated) fully agree with the 
subspecies, but the greatest breadth of the carapace only very slightly 
exceeds its length; only in the case of the adult QO the proportion is 
the same as in Nobili’s subspecies. As to the fourth point of difference 
here named, 3 specimens show, that the breadth of the front is nearly 
wholly as long as the posterior margin of the carapace; only the adult 
© has the posterior margin distinctly longer, but it is this very character 
de Man (1896) points out as existing between Ses. rotundata (= ©’) and 
Ses. dentifrons (=), and it must be regarded as a sexual difference. 
As on a whole my specimens take an intermediate position between 
the type and Nobili’s subspecies, though they do indeed approach the 
latter, I am-inclined to drop this subspecies, the characters of which do 
not appear important enough to maintain its distinctness. 
Another question, whether Ses. oceanica de Man is a distinct species, 
or merely a young stage of Ses. rotundata (which latter supposition has 
been advanced by de Man himself in 1891), must now be discussed. 
Besides by its smaller size Ses. oceanica is distinguished by the following 
characters : 
1°. The length of the carapace is less in proportion to the distance be- 
tween the external orbital angles. 
2°. The front is somewhat lower, its height being not yet a third of its 
breadth. 
3°. The lateral borders of the carapace are somewhat less curved. 

Now, if we take the distance between the external orbital angles = 
100, then the length of the carapace is in different specimens, arranged 
according to this latter dimension: 
114 in & (length of carapace 15.25 mm.). Ses. oceanica de Man 1889. 
116 in Q K = . i251. 2 x id 5 2 
121 ins Z z ‘i 7 Bs P . Ld SSO}: 
(Museum sp.) 
122 Init a . X 24.5 Bs Ses. rotundata. Museum sp. 
from Nias. 
131 in QO # e ks 32:— 3 cs Nobili, 1899, 
p. 269. 
