382 Records of the Indian Museum. [Wor Shik 
Group III. 
. lowtst, sp. nov. 
. pilosus, sp. nov. 
. candidus, sp. nov. 
. plebs, sp. nov. | 
pods comparatively well developed 
in male, reduced in female. Appen- 
dix interna present on all four pairs 
in male, but entirely absent in female. 
| Endopod of last four pairs of pleo- 
nef nels 
Group IV. 
Endopod of last four pairs of pleo- 
pods large and well developed in 
P. sabsechota, Kemp female, quite rudimentary in male. 
Appendix interna absent in both 
sexes. 
Group V. 
Endopod of last four pairs of 
\ pleopods much reduced in both 
} sexes. Appendix interna absent 
‘in both sexes. 
P. bispinosus, Hailstone 
and Westwood. 
P. trispinosus, Hailstone. 
P. echinulatus (M. Sars), P. victorrensis, Fulton and Grant, P. 
hendersont, Kemp, and P. parvirostris, sp. nov., represented in the 
Museum collection by examples of one sex only, also in all prob- 
ability belong to this group. 
In Group I the appendix interna is usually tipped with a series 
of small coupling hooks, which are ill-developed or absent in other 
sroups that possess this appendage. In Group V the separation of 
a distinct segment at the base of the endopod is clearly marked, 
whereas in Group I the division is obscurely indicated.! 
P. sabsechota, the sole species comprised in Group IV, is appa- 
rently an abnormal form, the distinction between the sexes in the 
size of the endopad being the reverse of that found in any other 
species which in this respect exhibits sexual differences. The re- 
maining groups clearly form a morphological series characterised 
by the progressive reduction of the endopod and by the reduction 
and suppression of the appendix interna. Group I in which the 
pleopods have retained their full development is clearly the most 
primitive, while Group V in which they are more reduced than in 
any other is the most specialised. It is noteworthy that Group I 
includes all the deep-water forms in the collection. 
The facts are not only of interest in the light they throw on 
the development of the species within the genus; they also, as it 
appears to me, form a valuable clue to the evolution of the family 
as a whole, for the other genera can be divided into two sections 
agreeing, respectively, in the development of their pleopods with 
| Cf. Wollebaek, Bergens Museums Aarbog, 1908, no. 12, p. 44, text-fig. 2. 
