1612 THE VOYAGE OF H.M.S. CHALLENGER. 



peraeon answering to the side-plate. Fig. 2 is stated to be the head of the female, 

 ten times the natural size, with the mandible. Since, however, the mandible has a 

 three-jointed palp, the specimen was no doubt a male, although, to judge by the 

 anterior antennae, a young one. In both specimens the mandibular palp is figured as 

 perfectly straight, not with the two short terminal joints forming a sickle-like curve, 

 the curvature probably being developed only at a more advanced period of life than 

 that which either of these specimens had attained. 



Rhabdosoma brevicaudatum, n. sp. (PL CCVIIL). 



Rostrum broken, the remaining portion with the neck and ocular region a quarter 

 of an inch long, the neck being by itself one-tenth of an inch ; in front of the 

 mouth organs there is a strongly projecting tooth or process on the ventral surface at 

 the base of the head ; the peraeon about three-twentieths of an inch in length, with 

 the dorsal outline convex, the first segment short, the second longer than the first, 

 but shorter than any of the following, the seventh not much shorter than any of the 

 four preceding segments ; the first three segments of the pleon together as long as 

 the peraeon, the postero-lateral angles of the first acute, but not produced backwards, 

 those of the second very slightly produced, those of the third very acute and much 

 produced backwards, the lower margin of the third segment being much more convex 

 than that of the two preceding segments ; the remainder of the pleon to the end of 

 the telson equal in length to the first three segments, but to the end of the uropods 

 measuring a quarter of an inch ; the fourth segment about half the length of the 

 following double- segment. 



Upper Antennse placed in the ventral groove of the head just in front of the oval 

 ocular region ; the first joint of the peduncle considerably longer than the second ; the 

 one-jointed flagellum longer than the peduncle, the distal margin carrying a few 

 filaments. 



Lower Antennse wanting. 



Mouth Organs not well observed ; the MaxiUipeds appear to have the outer plates 

 apically pointed ; the Mandibles without palp. 



First Gnathopods very short ; the first joint with sinuous front and convex hind 

 margin; the second joint broader than long; the third joint a little longer than the 

 second, distally widened; the wrist large, widest where it joins the hand, the hind 

 process longer than the proximal part of the joint, and longer than the hand, ending in 

 a sharp apical tooth, a little way above which a piece of the hind margin is finely 

 denticulate, the inner or front margin of the process being similarly denticulate ; the 

 hand has a very convex front margin, the hind margin beyond the neck being slightly 

 convex and distally a little denticulate, the distal margin finely pectinate and supplying 



