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



the caudal shield is excavated posteriorly, the postero-lateral margins being prolonged 

 beyond the articulation of the uropoda, but in lanthe the excavation is deeper. 



Certain species of Janira already described by myself in the present Report (p. G) 

 have a mandibular palp, and the same structure is present in Janira maculosa. I cannot 

 therefore admit that the presence or absence of a palp to the mandible is any safe criterion 

 of generic distinction. The only structural feature in which lanthe differs from Janira 

 is in the want of an articulated scale — the rudimentary exopodite — upon the antennae. 

 In pi. i. fig. 7 of his Memoir, Bovallius figures the antenna of Iantltc speciosa, and it 

 may be seen from that figure, as well as from the description, that the third joint of the 

 peduncle is furnished with a stout spine on the outer side in a position exactly corre- 

 sponding with the exopodite. In the figure this spine is represented as being articulated, 

 and in a species presently to be described, I shall refer to a similar spine having an 

 exactly similar position, being fixed to the third joint of the peduncle, and separated 

 from it by a joint. In any case it appears to me to be a matter of impossibility to dis- 

 tinguish exactly between such a spine and the articulated scale of Janira or Stenetrium. 



A second species of Isopod has been referred to this same genus by Studer, in his 

 account of the Isopoda collected by the German exploring vessel " Gazelle." Studer's 

 description of this form rests upon the examination of a single imperfect specimen from 

 Kerguelen. The Challenger during its long stay at Kerguelen obtained a very large 

 number of specimens of this Isopod, which was named by Studer lanthe bovallii. I cannot 

 however, agree with Dr. Studer in regarding this species as closely allied to Bovallius's 

 species. It certainly agrees with it in the general shape of the body even more than is 

 apparent from Studer's figures, since there are two rows of blunt tubercles along the back 

 instead of only a single row as represented by this author. The antennary organs arc- 

 very different ; the first pair of these or the antennules are much more like those of 

 Jsera in the shortness of the flagellum, which consists in my specimen of only four or 

 five joints, whereas in lanthe speciosa, as in Janira, the flagellum is long: this difference 

 is noted in the figure by Studer. The flagellum of the antenna as correctly figured by 

 Studer is proportionally short; with regard to the rudimentary exopodite there is a conical 

 spine on the third joint which seems to me to be the equivalent of this structure. 



The most marked difference, however, apart from the antennules, is the form of the 

 uropoda, which were wanting in Studer's specimen. These are displayed in fig. 8 of 

 PI. V.; the basal joint is extremely long, the two distal joints short, (he endopodite 

 being larger than the exopodite; it has been already mentioned that in lanthe speciosa 

 the uropoda are precisely similar to those of Janira in that the two rami are subequal to 

 each other and to the basal joint. Again the first thoracic appendages in neither sex of 

 lanthe bovallii are modified into a prehensile hand. In view of these differences it i.s 

 in my opinion necessary to distinguish gcnerically lanthe bovallii from lanthe speciosa, 

 and whether there is or is not (in my opinion not) any necessity for a new generic term 



