19 



extremities, one above and one below the point of attachment 

 to the hind margin of the carapace. Each of the large median 

 keels on the first five terga is in the form of a broad spine which 

 curves forwards. The pleura of the first segment are very small. 

 In the second segment they reach their greatest development ; 

 they overlap the pleura of the segment in front and also those 

 behind. The pleura become successively narrower and shorter 

 in the posterior segments. Each pleuron has a curved midrib 

 which springs from the thickened pleurotergal suture. All 

 the pairs of pleura are fringed with setae. On the terga of the 

 second to fifth segments there is on each side an oblique furrow 

 running from the postero-lateral angle towards the median 

 keel. 



The telson has a slight median ridge and tapers to a fine point. 

 The eyestalks bear a small, blunt tubercle on the anterior 

 margin. Occasionally it is almost absent, and apparently is 

 not present in Indian specimens (Alcock, 1901). At the posterior 

 end of the orbital sinus there is a small part which appears 

 almost translucent, whereas the rest of the impacted eyestaik 

 is hard and opaque. Smith (1882) suggests that this may re- 

 present an old corneal area, and that there was another one 

 at the tip of the lateral process of the eyestaik. 



The antennules are very like those of P. typhlops, but the 

 scale is narrower and much longer than the peduncle, and has 

 no teeth on its inner margin. The inner flagellum is very slightly 

 longer than the antennae, and is also longer than the carapace. 

 The outer flagellum is very short and slender, only slightly 

 longer than the scale. There are two spines at the outer distal 

 angle of the basal peduncular joint. The outer flagellum has a 

 dense fringe of setae on its distal three-fourths. 



The antennal scale is longer and more sharply pointed than 

 in P. typhlops. It reaches almost to the tip of the peduncle 

 and is furnished with setae on both edges, as are also the pedun- 

 cular joints. 



The mouth parts are practically identical in structure with 

 those of P. typhlops. 



The chelipeds Vary from about two and a -half to three times 

 the length of the carapace. All the joints are flattened, especially 

 the merus and ischium. There are one or two spines on the 

 proximal half of the upper border of the merus, and one at the 

 distal end of the same joint ; the lower margin is very minutely 

 spinulose, sometimes alm_ost smooth. The carpus has an upper 

 and a lower distal spine. The lower border of the propodite 

 is spinulose. 



The other pairs of pereiopods are similar to those of P. 

 typhlops. The fifth are chelate in the female, while in the male 

 the fixed finger is much shorter than the dactyl. 



Neither the pleopods nor the uropods present any important 

 differences from those of P. typhlops. 



Size. — The largest specimen taken by the Helga is 75 mm. 

 long. Alcock gives the length of one of his largest specimens. 



