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



Remarks. — This genus is evidently most nearly allied to lanthopsis and Acanthon- 

 iscus, and it may be that I am wrong in distinguishing it. It differs, however, from 

 the latter in a number of particulars, notably in the biunguiculate thoracic appendages ; 

 these appendages in Acanthoniscus terminate in a single claw ; as this character 

 undoubtedly distinguishes other genera, it is perhaps permissible to make use of it to 

 distinguish Iolanthc from Acanthoniscus, although the two forms show very gxeal 

 resemblance, particularly in the shape of the uropoda. From lanthopsis the present 

 genus differs in the absence of eyes and in the long straight epimeral spines as well as in 

 the form of the antennules with their long flagellum. 



Iolanthc acanthonotus, F. E. Beddard (PL IV. figs. 9-14; PI. V. figs. 1-4). 

 Iolanthe acanthonotzis, F. E. Beddard, Proc. Zool. Soc. Lond., 1886, pt. i. p. 104. 



This species is represented by a single female specimen, dredged to the South of 

 Kerguelen in 1675 fathoms. 



It is an extremely large species compared with its allies, measuring 24 mm. in length. 



This species is remarkable for the immense length of the spiniform lateral prolongations 

 of the thoracic segments, which is an exaggeration of the characters found in lanthopsis 

 bovallii. In other respects it presents a very close agreement with that species. 



The head is as wide as the succeeding segment of the thorax, its margins are prolonged 

 on either side into two spines, of which the anterior is very much the longer ; the central 

 region of the head is very convex, while the curved anterior margin is prolonged in the 

 middle line into a long spine, which is directed forwards and upwards. There is no trace 

 of eyes. 



The first three segments of the thorax are concave anteriorly and convex posteriorly ; 

 the fourth is almost straight, the three posterior segments being concave posteriorly, 

 the amount of the curvature of the segments increasing progressively. The antero- 

 posterior diameter of all the thoracic segments is about equal. In the dorsal median 

 line of each of the thoracic segments is a stout and long vertically directed spine ; in the 

 four anterior segments the spine arises near to the anterior margin of the segment ; in 

 the three posterior it arises near to the posterior margin. The general surface of the 

 body, including the dorsal and lateral spines, is sparsely covered with long hairs. 



The first segment of the thorax as already mentioned is no wider than the head, but 

 the remaining segments of this region are rather wider and subequal. The curvature of 

 the segments, however, causes the outline of the body to be more or less oval, though the 

 posterior segments are in reality fully as wide, measured from tip to tip, as the anterior 

 segments, or even wider. The lateral margins of the first thoracic segment are proloi i ■_ 

 on either side into a longish spine, which is distinctly shorter than the anterior of the 

 two lateral spines of the head. 



