34 THE VOYAGE OF H.M.S. CHALLENGER. 



Neasdlus kerguelenensis, F. E. Beddard (PL II. fig. 11 ; PL III. figs. 1-6). 



Neasellus herguelmmm, F. E. Beddard, Narr. Chall. Exp., vol. i. p. 882, fig. 32G, 1885. 



The single specimen belonging to this new species and genus has already been 

 briefly described and figured by myself in a notice of the Isopoda collected during the 

 voyage, published in the first volume of the Narrative. I have also referred to it as to 

 the other new species of Isopoda in a Preliminary Report communicated to the Zoological 

 Society of London. 



The extreme length is about 2 mm. 



The body is broad and convex ; the general outline is pear-shaped owing to the 

 great breadth of the head and of the two anterior segments of the thorax. 



The head is immensely extended laterally, and its shape reminds one very forcibly of 

 that of the hammer-headed shark; only about the middle third of the head is articulated with 

 the first thoracic segment, the lateral regions are separated by deep curved incisions ; the 

 central region of the head is convex, the lateral regions are flattened; the anterior margin 

 of the head is curved, convex in the middle region and concave laterally ; the lateral 

 margins are notched where the antennules articulate ; the antennae are covered over at 

 their insertion. The whole of the anterior and lateral margins of the head are fringed 

 with peculiar spines, which are flattened and somewhat conical in form, often curved; they 

 are placed close together, no interval being left between two adjacent spines; the posterior 

 margin of the head (bordering the lateral incision) is quite smooth and free from spines. 

 The dorsal surface of the head is also quite smooth. 



Eyes are completely absent. 



The two first thoracic segments are together about equal in length to the head in its 

 middle region. The line of suture which separates these two segments from each other is 

 obliterated except for a short space laterally. The width of both these segments is slightly 

 greater than the width of the head ; laterally both of them project as rounded spatulate 

 processes fringed with spines similar to those upon the head ; the anterior forward concave 

 margin of the first segment is, like the posterior margin of the head, free from these 

 spines. 



The remaining segments of the thorax are subequal in length, and about one-fourth of 

 the length of the conjoined anterior segment ; judging from the separated lateral regions 

 of the two first segments, the second of these would be about equal to the following 

 segments. 



The third, fifth and sixth segments have long oval lateral processes like those of the 

 anterior segments, and like them also fringed with spines ; the diameter of these segments 

 is not less than that of the first two ; the lateral regions of the sixth segment are more 

 bent backwards ; in the fourth and seventh segments of the thorax the lateral regions do 



