CRUSTACEA OF THE MERGUI ARCHIPELAGO. 15 
distinguished by the longer spines of the rostrum, and from 
Herbst’s species moreover by the direction of these spines. 
The cephalothorax is subpyriform, triangular, much more nar- 
rowed anteriorly than the cephalothorax of H. oryx, A. M.-Hdw., 
and even a little more than that of H. Pletone. In the largest 
specimen (which I am describing) the proportion of the length* 
of the cephalothorax to the distance between the external angles of 
the orbits is as 9 to 4, whereas in _H. Pleione itisas5 to 2. In the 
new species the proportion of the length of the cephalothorax to 
the breadth(measured a little before the lateral epibranchial spines, 
where the carapace is broadest) is as 15 to 13. The gastric and the 
anterior cardiac regions are each elevated into a convex, rounded 
tubercle, both of which are about equally prominent. Between 
these two tubercles a small median transverse tubercle occurs 
in H. Pleione, which is not found in this species. The posterior 
cardiac region also rises into a small blunt median tubercle, 
directed obliquely backwards, and on each side of it an elevated 
line is observed running parallel with the posterior margin 
of the cephalothorax. 
In H. Hilgendorfi there is no median longitudinal series of 
spines on the upper surface of the cephalothorax. In H. Pleione, 
on the contrary, the posterior cardiac region rises into an 
acute spine. Immediately behind the imaginary line which 
unites the fissures of the supraorbital margins with one another, 
in H. Pleione five small, blunt, semiglobular tubercles or spines 
are found on the anterior declivity of the great gastric tubercle, 
arranged in an arcuate line; in our new species only the two 
lateral tubercles of this group are found, while the three middle 
ones are almost completely wanting. The epibranchial spine, 
with which each side of the cephalothorax is armed behind the 
middle of the lateral margins, in our species is comparatively 
much stronger, acute, and curved upwards; an imaginary line, 
which unites the bases of the two epibranchial spines with one 
another, crosses the posterior declivity of the anterior cardiac 
region. Between the anterior cardiac tubercle and the epi- 
branchial spines two small, scarcely prominent, blunt tubercles 
are found on each side of the former, lying in an oblique 
direction; two imaginary lines, which unite the tubercles of 
* The length of the carapace is the distance between the posterior margin of 
the cephalothorax and a transverse imaginary line, which unites the anterior 
angles of the supraorbital margins. 
