180 A HISTORY OF RECENT CRUSTACEA 



CHAPTER XII 



TRIBE II. THALASSINIDEA 



THE carapace is short and compressed, with little or no 

 rostrum. The last segment of the trunk is articulated 

 with the preceding. The eye-stalks are small. Both pairs 

 of antennas have long peduncles. Of the trunk-legs the 

 first pair are perfectly or imperfectly chelate, the last pair 

 are short, more or less abnormal, directed backwards. 

 The pleon has the segments not overlapping, with the 

 side-plates feebly developed and having their hinder angles 

 generally rounded. The pleopods are long, biramous, 

 variable ; the swimming fan is strong. The branchiae vary 

 in number and form. 



In this tribe are included four families, the Thalassi- 

 nidas, Callianassidas, Axiidas, and Thaumastochelidas. The 

 division of the Macrura adopted by the late Mr. Spence 

 Bate, into Trichobranchiata, in which the branchial plumes 

 are made up of long cylindrical filaments, Phyllobranchiata, 

 in which the plumes are formed by a series of foliaceous 

 plates, and Dendrobranchiata, in which the branches of 

 the various plumes divide and subdivide in an arborescent 

 manner, does not seem practically very convenient. It 

 has been alreadv seen that two families so intimately 



I/ V 



allied as the Paguridas and Parapaguridse would have to 

 be placed, the former in the Phyllobrarichiate, the latter 

 in the Trichobranchiate, division. But also in the present 

 tribe Spence Bate himself points out a weakness in the 

 arrangement, for of the genus Oallianassa he says : ' The 

 structure of the branchias of Oallianassa is so intermediate 

 in character that it may be claimed by anatomists as be- 



