384 Records of the Indian Museum. [Vol. XII, igi6.] 



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. Crangon 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-day in Crangon 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 monodactNdous condition of 

 these limbs in Sahinea and Prianocrangon 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 F^rco/^, 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 an}^ 

 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. 



1 Baker, Trans. Rov. Soc. S. Australia, XXVIII, p. 158 (i904». 



2 Nobili, Ann. Set'. Nat. Zool. Paris, (g), IV, p. 82 ( 1006). 



