384 Records of the Indian Museum. [Vou. XII, 1916.] 
primarily arisen from a form in which this limb was well developed 
and a priori it was not to be expected that the four genera had 
passed through a stage in which it was to some extent reduced. 
It is, however, difficult to see how it could have been other- 
wise. Cvangon and its allied genera might, indeed, have arisen 
independently from an ancestor of Pontophilus, that is to say from 
a form differing from Group I of that genus only in the possession 
of long second legs. In this case the pleopods must have evolved 
separately in the two instances ; with the result that their identity 
of structure, as we see it to-dav in Cvangon and the related genera 
on the one hand and in Pontophilus, Group V, on the other, is an 
example of convergence. 
I am inclined to think that this conclusion is erroneous. The 
tendency that clearly exists towards the reduction or suppression 
of the second pair of legs shows that these appendages are un- 
usually plastic in Crangonidae: the monodactylous condition of 
these limbs in Sabinea and Pricnocrangon is evidently an instance 
of convergence and affords no evidence of real affinity. The struc- 
ture of the pleopods is more likely to yield a trustworthy estimate 
of relationship. 
Of the genera Vercoia, Baker!, and Coralliocrangon, Nobili?, 
I have seen no examples. In the former, according to a sketch 
kindly sent me by Mr. Baker, the endopod of the last four pleo- 
pods is comparatively large, but without appendix interna. The 
genus has perhaps arisen separately from forms similar to those 
in Group III of Pontophilus ; it differs from all species of the latter 
in the monodactylous character of the second legs. Owing to lack 
of information regarding the pleopods, it is impossible to make any 
suggestion regarding the relationships of Coralliocrangon. This is 
particularly unfortunate, for the persistence in the genus of the 
linea thalassinica points to its being a survival of some very primi- 
tive form. 

| Baker, Trans. Roy. Soc. S. Australia, XXVIII, p. 158 (1904). 
2 Nobili, Ann. Sct. Nat. Zool. Paris, (9), 1V, p. 82 (1006). 
i 
