368 EEV. T. E. E. STEBBING ON NEW SPECIES OF AMPHIPODOUS 



to Rhahdosoma as the earliest name of the genus, and thus in a manner forced to 

 change the name of the family from Xiphocephalidae to Rhabdosomidae. 



Dr. Bovallius has very acutely unravelled the synonymy, and explained the distinctions 

 between the species hitherto included in the genus Rhabdosoma. These are Rhahdosoma 

 armatum (Milne-Edwards), 1840, Rhahdosoma, whitei, Spence Bate, 1862 (the Xyphi- 

 cephale of Eydoux and Souleyet), Rhahdosoma lilljeborgi (Bovallius), 1890, • and 

 Rhahdosoma brevicaudatum, of the 'Challenger' Eeport, 1888. Two new species, 

 R. piratum and R. brachyteles, are now instituted. 



Rhabdosoma pieatum, n. sp. (Plate LV. A.) 



The head is longer than the perseon and the iirst three segments of the pleon, as long 

 as the whole pleon to the extremity of the uropods. The slender rostral part is nearly 

 double as long as the part behind the first antennae. Of the perseon-segments the 

 fourth, fifth, and sixth are the longest. The first three segments of the pleon have the 

 postero-lateral angles acute. The third is a little longer than either of the first two 

 or the fourth, but a little shorter than that which is formed by coalescence of the fifth 

 and sixth. The narrow tapering telson is considerably longer than any of the preceding 

 segments, and reaches a little beyond the first uropods. 



The eyes are of the character usual in the genus. 



The first antennae are very small, two-jointed, tipped with four short filaments. 



No second antennae were apparent in the specimen. 



The first gnathopods are as usual minute, the second joint a little sinuous, the 

 fourth scarcely larger than the third, the fifth sharply produced behind as far as the 

 minutely toothed apex of the hand, which is narrower than the basal part of the wrist, 

 but about as long. The finger is slender, very slightly curved, more than half the 

 length of the hand. 



The second gnathopods differ little from the first, but have the process of the fifth 

 joint a little shorter, and the apical margin of the hand narrower. 



First perceopods. The second joint is rather wider but not longer than the fourth ; 

 the fifth is narrower and shorter than the fourth, to which the slightly curved sixth is 

 subequal in length though not in breadth. The finger is slender, curved, half as long- 

 as the preceding joint. 



The second peraeopods scarcely differ from the first, except in slightly greater length 

 of some of the joints. 



Third perceopods. The branchial vesicles are oval, more than half as long as the 

 second joint of the limb and much wider than it. No trace of branchial vesicles 

 could be perceived on any of the preceding limbs. In slenderness and general structure 

 the third are very like the first and second peraeopods, but they have the second, fourth, 

 and sixth joints much longer, and the second decidedly longer than the fourth. 



Fourth peroeo^pods. The branchial vesicles are a little longer than the preceding pair. 



