CUMACEA FROM THE COPENHAGEN MUSEUM. 31 



Family LEUCONID.E. 



The new genera which are described below render necessary some important 

 modifications in the definition of this family. While all the forms hitherto described 

 agree in having exopods on the first three pairs of legs in the female and on the first 

 four in the male, and in having two pairs of pleopods in the latter sex, the species now 

 described from New Zealand show that the thoracic exopods may be reduced to two 

 pairs in both sexes, and the male pleopods may be present as a single pair or altogether 

 absent. Further, the division of the endopod of the uropods into two segments may 

 be indistinct or suppressed. 



The fact that, in some of the species, the ischium of the second pair of legs is 

 distinctly developed (as in Zimmer's Pseudoleucon) cannot be made use of as a generic 

 character, since Ileteroleucon aJcaroensis and Lcucon (?) heterostylis present an inter- 

 mediate condition in which the segment in question is developed only as a very narrow 

 and incomplete ring of chitin between the basis and merus. I find the same structure 

 in Leticon nasica Kroyer, L. assimilis Sars, and L. longirostris Sars, and possibly this 

 vestigial segment has been overlooked in other members of the genus. I cannot 

 identify it, however, in the species of Eadorella and Eudorellopsis which I have 

 examined. It is noteworthy that the disappearance of the segment is thus shown to 

 be due to " excalation," not, as Sars says (Crust. Norway, iii. p. 29), to fusion with the 

 merus. 



In other respects, especially in the structure of the mouth-parts, the new forms 

 agree with the Leuconidae already known. The inconvenience of genera distinguished 

 only by the characters of one sex is sufficiently obvious, and indeed, in the case of one 

 of the species described below, I have been unable to decide as to its proper generic 

 position owing to the fact that no male specimens were found. Apart, however, from 

 the frequent use of such distinctions in other groups of animals, a precedent is afforded 

 among the Cumacea by Sars's genus HemilaviproiJS, which is distinguished from 

 Lamprops only by the characters of the male. 



The following key will serve to indicate the position which the new genera occupy 

 relatively to the other genera of the family : — 



A. First three pairs of legs in female and first four in male cany exopods. 

 a. Two pairs of pleopods in male. 



a. Autcnuules not geniculate Leucon Kroyer. 



b. Antennules geniculate between second and third segments of 



peduncle Eudorella Norman. 



c. Antennules geniculate between first and second segments of 



peduncle, 

 a'. Pscudorostrum obsolete or short, vertical, and truncated . . Eudorellopsis Sars. 

 b'. Pscudorostrum long, oblique, and acute Pseudoleucon Zimmer. 



