CIIUSTACEA OF THE MERGUI ARCHIPELAGO. 17 



obtuse angle with the anterior declivity o£ the gastric region. In 

 a. Pleione, on the contrary, the spines are directed more down- 

 wards, so that they are situated in the prolongation of the oblique 

 surface of the anterior declivity of the gastric region. When the 

 tips of the two rostral spines are united by an imaginary Hue 

 and the antero-internal angles of the supraorbital margins by 

 another, the proportion of the distance between these two 

 imaginary lines to the distance between the antero-internal angles 

 of the supraorbital margins is as 8 to 3 ; in the smaller female 

 individuals this proportion is as 5 to 3, because the rostral 

 spines are comparatively shorter. The basal antennal joint is a 

 little narrower in this species than in H. Pleione, and its external 

 margin is also of a somewhat different shape. In Herbst's 

 species the epistome is comparatively a little shorter, and it there- 

 fore appears a little more enlarged ; in this species (the male) 

 the epistome is Ig millim. long, and the distance between the 

 postero-internal angles of the orbits is 4| millim., and therefore 

 three times as broad as the length of the epistome. Immediately 

 behind the postero-internal orbital angles a small dentiform 

 tubercle is found, lying between these angles and the antero- 

 external angles of the buccal cavity. The penultimate joint of 

 the peduncle of the external antennae is twice as long as the ter- 

 minal joint. The outer maxillipeds and the male abdomen much 

 resemble those of H. oryx. 



The chelipedes are scarcely longer than the length of the 

 body (the spines of the rostrum included). The upper margin 

 of the arm is provided above, at the proximal extremity, with two 

 deniiform tubercles situated very near to one another. The 

 wrist presents a small tubercle at its internal anglej and one 

 or two on its upper surface. The hands are rather slender, 

 being nearly five times as long as high, the fingers (which are 

 about half as long as the palm) included. The scarcely sinuous 

 upper and under margins of the palm are parallel to one 

 another ; the hands are quite smooth and glabrous. The inner 

 edges of the fingers are minutely denticulate and a little gaping 

 at the base. 



The ambulatory legs much resemble those of S. oryx. Those 

 of the first pair are about once and a half as long as the whole 

 body, and the other legs are successively shorter ; so that the 

 ambulatory legs of the last pair are only once and one third the 

 length of the cephalothorax (exclusive of the rostral spines). 



LINN. JOUEN. — ZOOLOGY, VOL. XXII. 2 



