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CRUSTACEA OF THE MERGUI ARCHIPELAGO. 71 
most as only a subgenus of Neptunus. Hitherto four species of 
the subgenus Hellenus and three of Xiphonectes were known as 
inhabitants of the Indo-Malayan seas. 
Neptunus Andersont in its outer form and physiognomy 
appears closely allied to Neptunus (Hellenus) rugosus, A. Milne- 
Edw., from Australia; but it is distinguished by the arms of 
the chelipedes not bearing one but two spines It also greatly 
resembles Neptunus (Hellenus) hastatoides; but WN. Andersoni 
presents a much broader frontorbital margin in proportion to the 
length of the carapace, and the arms of the chelipedes project 
less beyond the antero-lateral margins of the cephalothorax than 
in that species. 
The upper surface of the carapace appears extremely uneven, 
as in IV. rugosus, for it is not only very much embossed, but 
many lobules even rise into more or less developed, slightly 
granulated tubercles. ‘Two slightly elevated tubercles are found 
on each protogastric lobe, and a somewhat larger tubercle is 
placed on the mesogastric lobe; behind the latter, two tubercles 
are observed on the cardiac region, placed in a transverse line 
close together, and more elevated than all the others. A single 
median tubercle occupies the middle of the intestinal region, 
and finally some other tubercles are placed symmetrically on the 
postero-lateral regions of the carapace. The whole surface is, 
moreover, covered with a short dense down, which, however, 
does not conceal the tubercles. 
As in N. rugosus, the frontorbital or anterior margin of the 
carapace is comparatively very broad in proportion to the length, 
the latter being nearly as long as the distance between the ex- 
ternal orbital angles. Unfortunately the left half of the frontal 
margin of our specimen is a little mutilated, so that I cannot 
describe exactly the form of the median tooth or teeth of the 
front; for, as in WV. rugosus, a single small median tooth may 
perhaps also be found in this species in the middle of the front, 
or there may be two very small teeth. In every case the median 
tooth or teeth are much smaller and project much less forward 
than the next teeth; the latter are triangular, a little acute, and 
project about as much forward as the epistome, but not so much 
as the internal lobe of the under orbital margin. These teeth 
are separated by a rather deep emargination from the small, 
obtuse, external angles of the front (internal orbital angles), 
which project still less forward than the median tooth, 
