REPORT ON THE AMPHIPODA. 1607 



strongly widened ocular region, which is followed by the long rostral spine. The 

 anterior antennae, which can be laid within a deep groove, end in the male with single 

 flagellum-joint, which in the female is lost, while on the other hand the third joint 

 of the peduncle of the female antennas is dilated (bauchig aufgetrieben) and furnished 

 with numerous olfactory filaments. The antennas of the second pair are similar to 

 those in Oxycephalies, five-jointed, the terminal joint extremely small. The three- 

 jointed mandibular palp of the male is elongate, linear, reaching to the front antennas. 

 The mouth-organs in general are as in Oxycephahis only that the movable part of the 

 upper lip projects shield-like, and the mandibles armed with cutting edge are more 

 considerably shortened. The front limbs are short, complexly chelate. In the third 

 and fourth, and even the fifth, 1 peraeopods the first joint is narrow and linear, only the 

 first joint of the fifth is a broad plate of pear-shaped outline, to which I uniformly 

 failed to find any terminal joints attached. Curiously in the male only the third 

 and fourth peraeopods have branchial vesicles, while in the female also the branchias of 

 the three preceding pairs are retained. Also another obviously striking sexual distinc- 

 tion is observable in the appendages of the peraeon, in that especially the first and 

 second peraeopods, but also the following pairs, in the female have much stronger and 

 thicker first and third joints. The first three segments of the pleon are very extensive 

 and at least of the length of the whole peraeon. The pleopods are distinguished in the 

 male by the thickness and strength of their peduncles, which in the female are weaker 

 and more slender. The following hinder section of the pleon is linear, in the female 

 far more elongate. The eggs are developed in the pouch of the breast protected 

 between the side-wings of the peraeon-segments." 



The large third joint of the upper antennae, which Claus regards as part of the 

 peduncle, in this Report is considered to belong to the flagellum. It will be seen in 

 the account of Rhabdosoma brevicaudatum that in that species the fifth peraeopods 

 appear to have a minute appendage to the first joint. The first three pleon-segments 

 may occasionally be shorter than the peraeon. 



Rhabdosoma armatum (Milne-Edwards). Specimen A. 



1840. Oxycephahis armatus, Milne-Edwards, Hist. Nat. des Crustaces, t. iii. p. 101. 



1847. Rhabdosoma armatum, White, List of Crust, in Brit. Mus., p. 130. 



1848. „ „ Adams and White, Zool. of Voy. of H.M.S. "Samarang," p. 63, 



pi. xiii. figs. 7, 8. 

 1858. Macrocephalus longirostris, Spence Bate, Ann. and Mag. Nat. Hist., ser. 3, vol. i. p. 361. 

 1862. Rhabdosoma armatum, Spence Bate, Brit. Mus. Catal. Amph. Crust., p. 344, pi. liv. fig. 6. 



1 As this seems contradictory to what immediately follows, I may be mistranslating the original, which is, " An 

 dem funften und sechsten, auch siebenten Beinpaare, bleiben die Schenkelglieder schmal und stabformig, nur das 

 Schenkelglied des siebenten Beines ist eine breite Platte von birnformiger Umgrenzung." It will be remembered that 

 the fifth, sixth, and seventh limbs of the original correspond respectively to the third, fourth, and fifth peraeopods of 

 the nomenclature used in this Report. 



