’s RIJKS MUSEUM VAN NATUURLIJKE HISTORIE — LEIDEN. 197 
135 in J (length of carapace 33.— mm.) Ses. rotundata. Nobili, 1899, p. 269. 
123.3% 2 si e c Bsa) oes %, be Siboga sp. 
BATT. tte tame i ate) se ae s HW ye; 
BHR ioe es sae Wk hee ‘ ; 
Lae AO AN | pee Bi = de Man 1895 (type- 
sp. of dentifrons). 
‘ot AOL AS ee eae ie ‘ de Man 1895 (type- 
sp. of rotundata. 
We, then, conclude, that the length of the carapace, in proportion to 
the distance between the external orbital angles, increases with age 
and more so in the of than in the Q; it is this latter sexual dif- 
ference which has been put forth by de Man (1896). 
As to the second point of difference, de Man (1896) has already 
shown, that in Ses. dentifrons (= QQ) the front is lower, in proportion 
to its breadth, than in Ses. rotundata (= ©) '), and it is natural to sup- 
pose, that young ©’, such as are referred to Ses. oceanica, show the 
character, peculiar to the female sex. 
That in Ses. oceanica the lateral borders of the carapace are somewhat 
less arched may, in my opinion, be ascribed to, its being not yet full- 
erown; indeed, in the Museum specimen from Nias the curvature of the 
lateral borders is less pronounced than in quite adult specimens, but more 
so than in the true oceanica-specimen, which is somewhat smaller. 
Besides, de Man (1889, p. 430) observed in Ses. oceanica near the 
free margin of the front four tubercles, corresponding with the four slight 
emarginations of this margin, at least in the o’, and this very character 
has been found back by me, in oj and Q of the adult ,Siboga’’-specimens 
of Ses. rotundata. 
Concluding, I cannot admit Ses. oceanica as a distinct species, and | 
think, that more material, if available, will confirm my surmise. 
” ” ” 
138). 
” ” ” 

Dimensions : 1 2 3 4 
‘ot < O O 
st ) ¢ Y) 
Distance between external orbital angles . 29.5 ° 28.5  27.— 20.— mm. 
bs “4 second epibranchial teeth 36.— 35.— 32.5 24.— , 
Greatest breadth of carapace. . . . . 40. 40. 35. 25. ae ee 
enethNoricarapace... 42 <4. «ive. d¢.—) 30.0) jadeADi 1 A4 > 1. 
BreadchmOnmsiront. A. epee ies eee eon: Aino) lp. elon s 9:o ae 
ere htwoty tt Ontivat, same es- Is Msc 420 4.5 ABZ, Qe 
Breadth of posterior margin of carapace. 12.75 13.— 13.75 9.5, 
1) I have found, however, no difference, in this respect, between the two sexes. 
