366 DE. W. T. CALMAN ON NEW OE EAEE 



Family DIASTYLIDiE. 



Dr. C. Zimmer lias lately (Cumaceen der Deutschen Tiefsee-Exp. p. 181, 1908) 

 discussed in detail the classification of this extensive family. His re-definition of the 

 yenus Biastylopsis makes possible a more satisfactory allocation of a number of species 

 previously referred to Leptostylis, but there are indications that the grouping of the 

 species can be regarded only as provisional. Thus the general form of the body and 

 the disposition of the posterior thoracic somites, which Zimmer regards as the chief 

 distinguishing features of Biastylopsis, are repeated in some of the species of the new 

 genus Gynodiastylis described below, and that genus is linked, by the important 

 character of the third maxilliped, to the otherwise widely different Paradiastylis. 

 Again, Leptostylis thileniusi Zimmer is now referred by its describer to Diastylopsis ; 

 but it has a very remarkable structure of the third maxilliped not found in the other 

 species of the latter genus, and this structure, as I have pointed out (Ann. Mag. Nat. 

 Hist. (8) i. p. 239, 1908), is clearly derived from the simpler condition found in 

 Leptostylis insularuni, a species which, according to Dr. Zimmer's classification, would 

 fall into the genus Diastylis. On the other hand, the genus Leptostylis, reduced 

 Avithin the limits of a relatively precise definition by Zimmer's removal of various 

 species to other genera, must again overrun these limits to include L. wcdkeri 

 (Caiman, Bull. Mus. d'Hist. Nat. Paris, 1907, no. 2, p. 121), which, by its well-armed 

 telson, infringes the leading character of the definition. 



Of Diastylis, which still includes the majority of the species of the family, 

 Dr. Zimmer finds it impossible to give a satisfactory diagnosis — " Man kann einfach 

 sagen, dass Diastylis diejenigen Diastylidenarten umfasst, die in keine der anderen 

 Gattungen passen." As a matter of fact, the species included in Diastylis differ 

 among themselves in characters which, in some cases, seem as important as those 

 distinguishing the other genera, although without the discontinuity which renders 

 easy the definition of generic groups. 



The limits of the family itself tend to become indistinct. Thus, as Dr. Zimmer 

 remarks, it is, with our present knowledge, very much a matter of taste whether 

 Pseudodiastylis is to be referred to the Diastylidse or to the Lampropidae, and the 

 new genus Colurostylis has the form of telson characteristic of the PseudocumidEe, 

 while the characters excluding it from that family are neither numerous nor very 

 weighty. 



Key to Genera o/'Diastylidae. 



A. No pleopods present in male sex. (Third maxilliped witliout 



exopod in female.) Gynodiastylis, g. n. 



B. Two pairs of pleopods in male sex. 



a. Tliird maxilliped without exopod in female Paradiastylis Caiman. 



