858 MRS. E. W. SEXTON ON AMPHIPODA [NoV. 23, 



Stebbing). Between the characters of this genus, as given by 

 Sars, 1. c. p. 357, and those given by Ohevreux for Datiizenbergia 

 I can find no essential difference ; on two points only do the 

 accounts vary — viz., the lower lip and the telson, and of these, 

 the first is due to misapprehension on Chevreux's part, and the 

 second, the difference in the shape of the telson, is only a cha- 

 racter of specific value, and not of sufficient importance to justify 

 the creation of a new genus. Chevreux founded his genus on a 

 single specimen, always an unsafe proceeding, for even if, as in 

 this case, the specimen be sexually mature, yet as these animals 

 pass through several stages of development after reaching maturity 

 (see Rhachotropis helleri), the presence of the incubatory pouch is 

 no guarantee of its being fully adult. All the parts undergo more 

 or less modification, a.nd therefore characters drawn from a young 

 specimen are of no vahie as distinguishing specific features. 



Description. — 5 specimens were taken by the ' Huxley,' measur- 

 ing 3 mm., 5 mm., 5 mm., 5*5 mm., and 7"5 mm., respectively, all 

 females. Thiee marked stages of growth are shown : I immature ; 

 3 young females about the same stage of development as Chevreux's 

 specimen (as will be seen by a comparison of his figures with 

 mine) ; and 1 larger specimen older than the others, as shown 

 by the further modification of the second gnathopod. The 

 description of the male is taken from the type specimens of 

 Farapleustes megacheir Walker, which, through the kindness of 

 Dr. Scharff, I have been able to examine ; the larger specimen 

 measured 11 mm., the smaller 7 mm. 



The body is compressed, smooth, almost pellucid, cuticle 

 exceedingly thin ; segments well-defined. Perfeon and 1st 

 three pleon segments evenly rounded ; 4th pleon segment 

 with a marked dorsal depression. Chevreux in his first account 

 says " les trois premieres segments de I'abdomen presentent une 

 legere carene " : this statement is omitted in his later woi'k, and 

 the pleon is figured as perfectly smooth and rounded. Owing to 

 the transparency of the cuticle permitting the underlj'ing terga of 

 the 2nd and 3rd pleon segments to show through the overlapping 

 posterior edges of the segments preceding them, a curious de- 

 ceptive effect of dorsal teeth is produced with transmitted light 

 (see fig. 8). Walker in describing the male (P. Qnegacheir) says 

 " second segment of pleon (metasome) having a small dorsal 

 tooth," but in both sexes all the posterior margins are evenly 

 curved and entire. 



In the young specimens the first three pleon segments have 

 each a small tooth at the postero-lateral corner ; in the large 

 specimens only the 2nd and 3rd are thus provided, and in a less 

 degree than in the young ; inferior margin of the 3rd segment 

 in all, strongly curved. 



Side-jdates. — In the female the first four are Subequal in 

 depth ; 1st produced anteriorly in an acute lobe, covering the post- 

 antennal corner ; the 4th the broadest, lightly excavate behind ; 

 5th and 6th bilobed, much wider than deep. In the male, the 1st 



