SYSTEMATIC REPORT 163 



Remarks. In general appearance this species closely resembles M. gibbosa G. O. Sars from Euro- 

 pean and Mediterranean waters, which is characterized by the presence of two ' humps ' on the 

 carapace and a marked sigmoid shape in lateral view. The form of the antennae, eyes, rostrum and 

 tail-fan is very similar in the two species, but they may readily be distinguished by the much larger un- 

 equal protuberances on the carapace, by the less marked sigmoid shape of M. camelina, and parti- 

 cularly by the peculiar development of the first abdominal somite in this new species. In M. gibbosa 

 the first abdominal somite is larger and more robust than the succeeding somites, but there is no 

 prolongation of its posterior margin. The marsupium in M. camelina is unusually large and I can 

 count no fewer than twenty-three large eggs in the type specimen. It may be that the robust abdomen 

 and the peculiar strengthening of the first abdominal somite are correlated with the strain of supporting 

 such a relatively enormous load; the males may not show a similar modification. The form of the 

 mandibular palp is quite different from anything previously described in the genus, and had the other 

 appendages shown differences instead of close similarities, I should have felt inclined to found a new 

 genus for this remarkable new species. 



Distribution. The species has been taken on two occasions only, both from the same locality, in 

 somewhat shallow water near Simon's Town, False Bay, near Cape Town, South Africa. 



. „ „ c Genus Leptomysis G. O. Sars, 1869 



1869 Leptomysis G. O. Sars. 



Remarks. This genus can be distinguished from the genus Mysidopsis, which it very closely re- 

 sembles, by the form of the endopod of the first thoracic appendage, by the shape of the apex of the 

 telson and by the armature of the fourth pleopod of the male. In Mysidopsis, the third and fourth 

 segments of the first thoracic endopod are fused with no trace of a dividing suture, but in Leptomysis 

 the two segments are articulated in the usual way. In Mysidopsis, the exopods of the fourth pair of 

 pleopods in the male are longer than the endopods and the distal segment is terminated by a single 

 strong straight spinous seta. The setae on the other segments are of the normal slender plumose form. 

 In Leptomysis the setae of the distal three segments of the exopod of the fourth pair of male pleopods are 

 modified by being longer and slightly more plumose than those arming the other segments, and the distal 

 segment is terminated by a pair of long setae. In both genera this exopod is longer than the endopod. 



At one time, it was laid down as a generic character of Mysidopsis that the lateral margins of the 

 telson were armed with only a few more or less widely spaced spines, and this formed a useful dis- 

 tinction from the species of the genus Leptomysis. Owing to the addition of M. acuta and M. simihs 

 to the genus Mysidopsis, this definition has had to be modified, for in both these species there is a large 

 number of spines on the lateral margins of the telson. However, these spines are of equal size or are 

 graduated regularly, increasing in size distally, whereas in Leptomysis, the lateral margins of the telson 

 are armed with a very large number of spines, which are usually arranged in series of larger spines with 

 small spines in the spaces between them. The apex of the telson in Mysidopsis is (except in M. similis) 

 broader and less pointed than in Leptomysis, showing in some species either a median emargination or 

 a small unarmed cleft, whereas in all the known species of Leptomysis it is evenly and more narrowly 

 rounded. 



Only three species of Leptomysis are represented in the Discovery collection: L. apiops G. O. Sars, 



L. capensis Illig and L. megalops Zimmer. 



