CUMACEA FEOM THE COPENHAGEN MUSEUM. 367 



b. Third maxilliped with exopod in both sexes. 



A. Telson without spines. 



a. Telson very small, flattened; endopod ot uropods of two 



segments ; third and fourth legs with vestigial exopods in 



female Colurostylis, g. n. 



b. Telson larger, cylindrical; endopod of uropods of three 



segments ; third and fourth legs without exopods in 



female Pachystylis Hansen *. 



B. Telson with at least a pair of apical spines. 



a. Body of mandible abbreviated Diastyloides G. O. Sars. 



b. Body of mandible normal. 



a'. Pleural plates of third and fourth free thoracic somites 



expanded backwards ; third legs widely separated from 



second in adult female Diastylopsis S. I. Smith. 



b'. Pleural plates of thoracic somites not produced back- 



, , . T , , ,.-,,„, TDiASTYLis Say. 



wards ; third legs close to second m adult female ..It t, ^ o, 



l Leptostylis G-. O. Sars. 



C. Telson with a median apical spine Pseudodiastylis Caiman. 



Genus Gtnodiastvlis, gen. nov. 



Pleural plates of third and fourth free thoracic somites more or less expanded 

 backwards, third legs separated from second in adult female ; telson unarmed, 

 tubular, not produced beyond anus ; third maxillipeds without exopods in female ; no 

 pleopods in male ; endopod of uropods unsegmented or of two segments. 



Type-species G. carinata, sp. n. 



The name of this genus is intended to allude to the fact that the males resemble 

 the females more closely than in the other genera of the family. In the type-species 

 and in G. Icevis. the absence of exopods from the third and fourth pairs of legs 

 makes it difficult to distinguish between males and immature females f . According to 

 the precedents of Cumacean taxonomy, the presence of well-developed exopods on 

 these legs in males of G. costata and G. bicristata would be regarded as a distinction 

 of generic value, but in view of the close general resemblance between G. carinata 

 and G. costata it seems impossible, for the present, to place them in separate genera. 



Key to the Species of Gynodiastylis. 



A. No exopods on third and fourth legs of male. 



a. Carapace with six longitudinal ridges on each side. Endopod of 



uropods of two segments G. carinata, sp. n. 



b. Carapace smooth. Endopod of uropods unsegmented G. Icevis, sp. n. 



* See also the remarks on Diastylis (1) fistularis, sp. n., below. 



t The only other Cumacean of which the. males resemble the females in the number of the thoracic 

 exopods and in having no pleopods is Heteroleucon alcaroeasis (Trans. Zool. Soc. xviii. (1) p. 34, 1907). 



3d 2 



