390 A HISTORY OF RECENT CRUSTACEA 



type by having eyes, which are small but distinct, the 

 second antennae shorter, the second joint in the limbs of 

 the perEeon more dilated, and the pleon furry. In de- 

 scribing this species Mr. Chilton mentions that the third 

 pleopods have on the outer margin of the basal portion 

 ' an ovate appendage which perhaps represents the epipo- 

 diie.' He finds the males distinguished from the females 

 not only by the special organs at the base of the seventh 

 pair of limbs, but by rather stronger hands in the first pair, 

 and a clasping arrangememt in the last two joints of the 

 fourth pair. The female appears to have brood-plates on 

 the second, third, and fourth segments of the perseon. 



The figures in Plate XVI. are copied from the papers 

 iu which Mr. Chilton describes the two notable species 

 under discussion. 



While the mouth-organs and pleopods make Phreatoieus 

 an unquestionable Isopod genus, the affinity with the 

 Amphipoda appears not a little remarkable. The lateral 

 compression of the body, the downward lateral production 

 of the pleon-segments, the arrangement of the limbs of 

 the peraeon, the considerable development of the pleon, 

 the two-jointed branch in several of the pleopods, the 

 strong indication of a distinction between the sixth pleon- 

 segment and the telson, and above all the position and 

 structure of the uropods, form a group of characters which 

 bring this genus nearer to the Amphipoda than any other 

 Isopod can claim to be. In the limbs of the perseon the 

 third joint is not very short, as it usually but by no 

 means always is in the Gammaridea, nor does the fourth 

 joint in the first pair underride the fifth as is usual in the 

 gnathopods of the Gammaridea. On the other hand the 

 clasping arrangement of the fourth pair of limbs is 

 strikingly parallel to what is found in the Orchestiidse, 

 and, as Mr. Chilton points out, the expansion of the 

 second joint of the limbs in Phre.atoiciis australis is similar 

 to what is fojind in so many of the Amphipoda. In his 

 admirable discussion of all the characters Mr. Chilton is 

 inclined to disallow the Phreatoicidae any special proximity 

 to the Amphipoda, and is thus induced to remark that 



