REPORT ON THE ISOPODA. 33 



The difference of proportionate length between the antennas of this species and of 

 Pleurogonium albidum is brought about by the comparative shortness of the third joint, 

 which is not much longer than the second ; the fourth joint is also very short, the fifth 

 is extremely long. 



The first pair of thoracic appendages, as in other species of the genus, is modified 

 into a prehensile organ. 



Tristan da Cunha, 100 to 150 fathoms. 



Neasellus, F. E. Beddard. 

 Neasettus, F. E. Beddard, Narr. Chall. Exp., vol. i. p. 882, fig. 326. 



This genus is represented in the Challenger collection by a single small Isopod from 

 Kerp-uelen. 



Generic CJiaracter. — Body broad and flattened, wider anteriorly than posteriorly ; 

 surface of the body smooth dorsally, fringed laterally with numerous short flattened 

 spines. Head separated by a deep incision from the thorax and extremely wide, 

 eyes absent ; the antennae are situated at the extreme lateral margins of the head. 

 First segment of the thorax larger than any of the following, fused with the second 

 segment except laterally ; following segments of the thorax distinct and subequal, 

 separated by deep lateral incisions ; all the segments of the thorax, with the exception 

 of the fourth and seventh, with long rounded lateral processes. Abdominal shield 

 rhomboidal, notched at the apex, and laterally where the uropoda articulate. First pair 

 of antennae much shorter than the second pah', consisting of six joints of which the two 

 distal may be reckoned as flagellum ; antennae with a short flagellum about as long as 

 the distal joint of the peduncle. First pair of thoracic appendages modified into a 

 prehensile limb. Uropoda biramose, very short, like those of Pleurogonium. 



Remarks. — There can be no doubt that this forms a very distinct generic type. 

 Apart from the remarkable form of this Isopod, the great lateral extension of the head 

 with the antennae articulated at the extreme lateral margin and its separation by a deep 

 incision from the thorax, is quite a novel character ; moreover, the almost complete 

 fusion of the two first thoracic segments is a character quite new to the family 

 to which this genus evidently belongs ; in other respects it appears to come nearest 

 to Pleurogonium and Paramunna; in the articulation of the antennules below 

 the lateral extension of the head this genus recalls Leptaspidia, 1 where both pairs 

 of antennary appendages are quite covered by the head, arising altogether from its 

 lower surface. 



1 Westwood and Spence-Bate, Sessile-eyed Crustacea, vol. ii. p. 333. 

 (zool. CHALL. EXP. — part xlviii. — 1886.) Bbb 5 



