CUMACEA FEOM THE COPENHAGEN MUSEUM. 351 



In the case of N. zimmeri, the single female specimen was found in a gathering con- 

 taining numerous specimens of the male and no other Cumacea, so that there is every 

 probability that the two sexes do belong to the same species. In the richer gatherings 

 from the Gulf of Siam, however, two or three closely allied types of female frequently 

 occur in the same bottle with numerous males which cannot be satisfactorily dis- 

 tinguished from one another. 



The new species of which females are described below (N. zimmeri, N. gibhosus, 

 N. rejptans, N. minor, N. ico^dus, and N. agnatus) differ from the type of the genus 

 {N. unguiculatus) in having no exopod on the third maxilliped in that sex, and I find 

 that the female type specimen of N. suhmii G. O. Sars agrees with them in this 

 respect. The males of N. suhmii and N. zimmeri, however, have a well-developed exopod 

 on that appendage, and it may fairly be assumed that the males of the other species will 

 be found to have it also. The absence of this exopod in the female sex is already 

 known in several species of Diastylidse, and in that family it has been regarded as a 

 distinction of generic value. It might have been so regarded in this case also, were it 

 not for a further peculiarity presented by jV. reptans and iV^. tardus. The females 

 described under these names differ from all Cumacea hitherto known in having no 

 thoracic exopods at all ; they have lost not only that of the third maxilliped, but also 

 those of the first and second legs ; and, curiously enough, each of them was accom- 

 panied in nearly all the gatherings in which they occurred by another form hardly 

 differing from the first in any character of importance except in possessing exopods on 

 these legs. Both forms are represented by mature ovigerous females, and I have thought 

 it advisable to describe them under distinct specific names, but it must be admitted as 

 quite possible that li. repfans may be merely an individual variation or a phase in the 

 life-history of N. minor, and that N. tardus may stand in the same relation to N. agnatus. 

 At all events, the two pairs of species, if they are specifically distinct, can hardly be 

 generically separated ; and since the absence of exopods from the first and second legs 

 seems to be a distinction at least as important as the absence of an exopod from the 

 third maxilliped, there is no good reason for giving generic value to the latter character 

 and not to the former. 



I formerly gave as one of the distinguishing characters of the genus Nannastacus 

 the absence of a distinct ischium in the second maxillipeds (Fisheries, Ireland, Sci. 

 Invest. 1904, i. (1905) p. 23). In some of the species described below I find indications 

 of a separate ischium in this appendage, but as the character is one which it is difficult 

 to verify without undue sacrifice of material I should prefer to omit it from the generic 

 definition. 



As many of the species are known only in one sex it is not possible to give a 

 satisfactory key to their arrangement. I have attempted, however, in the remarks 

 appended to the description of each new species to indicate as far as possible its 

 systematic relations. 



3 B 2 



