CUMACEA FEOM THE COPENHAGEN MUSEUM. 307 



1). Third maxilliped with exopod in both sexes. 



A. Tclsoii without spines. 



a. Telsoii very small, flattened ; cndopod oF uropods of two 



segments ; third and fonrth Icj^s wilh 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. 



Ii. 15ody of mandible normal. 



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



expanded backwards ; third legs wicU-ly separated from 



second in adult female Diastvlopsis S. I. Smith. 



b'. Pleuj-al plates of thoracie somites not produced baek- 



, . , , , , • , , ^ , f DiAsrYLis Sav. 



wards ; third legs close to second in adult female . . "i t V, ^ o, 



I Leptostylis G. O. Sars. 



C. Telson wilh a median apical spine Pseudodiastvlis Caiman. 



Genus Gtxodiastylis, g-en. 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 unseginented or of two segments. 



Type-species G. carinata, sp. n. 



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

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

 and in G. Icvvis the absence of exopods from the third and fourtli 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. hicristata 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 



lU'opods of two segments G. cai'inatn, s\>. n. 



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



* See also the remarks on DiastijUs (?)Jistalaris, 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 Iffteroleucon aJcaroensis (Trans. Zool. Soc. xviii. (1) p. 34, 1907). 



3d :^ 



