CRUSTACEA FROM THE 'CHALLENGER' EXPEDITION. 31 



the first gnathopod they are even, very strong, and somewhat curved inwards ; there are 

 only hairs at the inner side, not on the lateral parts of the joints, which in the second 

 gnathopod have got three lines of hairs, and in the following ones five and six. In the 

 last three pereiopods there are not only lines of hairs on the lateral parts of these joints, 

 hut their point of attachment is strongly marked in the chitinous substance, so that 

 these joints look as if they were divided into five and six subjoints. And the same thing 

 is the case throughout with the fifth joint. Such subjointed pereiopods are also found 

 in Mysis, but not in any other genus of Schizopods. 



In the gnathopods as well as in the pereiopods the last joint is a short claw — even in 

 the first pair of the former, where it is wanting in Lophogaster. 



The Pleon and its Appendages. 



The abdomen has a length of 78 millims. It is square-shaped ; for its segments are 

 nearly as large as they are high. The second segment, for example, is 11 millims. in 

 height by 10 millims. in width. The edges of the segments are even ; only laterally 

 there are squamiform processes, which cover each other, and each of which has a rounded 

 anterior and a sharpened posterior portion. The shortest segment is the fifth ; the sixth 

 is much larger, and is divided by a deep sulcus into two parts, which look perfectly like 

 two distinct segments. One is the more inclined at first to think so, as the lateral squa- 

 miform processes, which terminate all the preceding segments, are attached to the first 

 of these two subdivisions. In the second one there are only two short spines on each 

 side. Sars has described something very much like this in Lophogaster ; and as we now 

 know that Nebalia, in which there are nine abdominal segments, has essentially schizo- 

 podal characters, while Gnathophausia in its unattached dorsal shield has decidedly a 

 phyllopodal character, this pseudo-amplification of the abdominal segments seems to me 

 to be exceedingly interesting, as it shows that Gnathophausia must be in genealogical 

 connexion with forms (or a descendant of forms) in which there are more than seven 

 segments in the pleon. 



The telson has a length of 30 millims. ; on its surface there is a longitudinal groove 

 bordered by two ridges ; the lateral borders of the telson are denticulated ; at its end 

 there are two spines, between which there is a semicircular cleft. The caudal appendages 

 are both jointed (PL X. fig. 2) ; the interior are somewhat shorter than the exterior ones ; 

 and both are shorter than the telson ; at their basal articulation there is a spine on both 

 sides. 



The five pairs of pleopods consist of a pear-shaped basal joint, at the posterior side of 

 which there is a protuberance ; at their inner side they are covered with a fringe of hairs. 

 The two annulated rami do not present any thing particular. Appendages such as have 

 been found here in the Euphausiidse do not exist in Gnathophausia. 



Before fixing the generic and specific characters of this large species, I shall now give 

 a shorter description of the smaller one (of which four specimens were got), and point out 

 especially the characters in which it differs from the larger one. 



