LARVAE OF DECAPOD CRUSTACEA 341 



Claus (1884) pointed out that the sternal artery of the Pagurid larva differs from that 

 of the "Macrura" so far as concerns the origin from it of the arteries to the maxilli- 

 pedes, and that, in this respect, Upogebia resembles the Pagurids. 



This suggestion of a separation of the Thalassinidea into two distinct groups involves 

 a cleavage within the family Callianassidae between the Callianassinae and Upogebiinae 

 which will not be readily accepted, and demands support by evidence from adult 

 structure. This evidence can, I believe, be given. 



In the first place I should point out that, especially in animals of burrowing habit, 

 such as these are, it is unsafe to attach much importance to general facies, and would 

 call attention, in illustration of the illusory nature of general form, to the independent 

 acquisition of the Crab form on quite different lines of evolution. 



The characters which unite the two subfamilies are given thus by Borradaile : 



(i) Linea thalassinica present, except in Callianidea} 



(2) Fixed antennal thorn present. 



(3) Antennal scale present, though vestigial. 



(4) Abdominal pleura small. 



(5) No suture on uropods. 



(6) No podobranchs on legs. 



The following differences between them are given by Balss : 



It is admitted that none of these additional differences seem very important, except 

 perhaps with regard to the maxillule. It is apparently characteristic of all Thalassinidea 

 that the maxillule has a coxal exite, but in Axius, Callianassa and Calocaris^ it is merely 



1 De Man (1928) makes a new subfamily for Callianidea. 



2 I have seen this exite in A. stirhynchus, C. macandreae, Thalassina anomala, and three species of Cal- 

 lianassa. I have not been able to examine Jaxea. 



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