326 PERCY SLADEN TRUST EXPEDITION 



The Pontoniinse are members of the Palsemonidse, the central and typical family 

 of the Carides. By the loss of exopodites and mastigobranchs from the legs, the 

 reduction of the gill formula, and the position of the last joint of the second 

 maxilliped at the side of the preceding joint, this family has discarded the primitive 

 organization which still prevails in such groups as the Pasiphseoida and the Hoplo- 

 phoroida. In the well-marked cleft of the mandible, the retention of the distal 

 "lacinia" of the maxilla, the shape of the legs of the first two pairs, with their un- 

 divided carpopodites and relatively unspecialized chelae, and in a certain absence of 

 exaggeration in all the features of the body, they appear more conservative than the 

 remaining members of the tribe, to some of which, indeed, and in particular to the 

 Crangonoida, it seems possible that their near ancestors may have given rise. 



The Subfamilies of the Palsemonidse. 



The members of the Palsemonidse fall into four groups, which we may rank as 

 subfamilies, defining them briefly by means of the following key : 



I. None of the bristles at the end of the larval telson become in the adult 

 transposed on to the anterior part of that organ, which is therefore unarmed on its 

 back and sides. The surface of the molar process of the mandible is closely ridged. 

 [There is a pleurobranch on the third maxilliped.] 



Desmocaridince Borradaile, 1915. 



II. Two pairs of the bristles at the end of the larval telson become in the adult 

 transposed on to the back of that organ. The surface of the molar process of the 

 mandible bears some half-dozen large knobs or crests. 



A. The end of the telson bears six spines. [There is no pleurobranch to the 



third maxilliped.] 



PontoniincB Kingsley, 1878. 



B. The end of the telson bears four spines and a varying number of feathered 

 bi'istles. I 



1. The side of the carapace is traversed by a suture. The outer flagellum 



of the antennule is but slightly cleft. There is no pleurobranch to the 

 third maxilliped. 



TyphlocaridincB Annandale and Kemp, 1913. 



2. The side of the carapace has no suture. The outer flagellum of the anten- 



nule is deeply cleft. There is a pleurobranch to the third maxilliped. 

 PaloBmonincB Kingsley, 1878. 



The peculiarities set forth in this key belong to all members of the subfamilies, 

 which by their means can be absolutely separated. In elucidating the relations of 

 the subfamilies to one another, however, account must also be taken of certain universal 

 characteristics by which the affinities of the groups are indicated. 



Of the four subfamilies, that of the Desmocaridinse is the most primitive, as has 

 been well shown by M. SoUaud, the describer of its only genus, Desmocaris^'. Among 



* C. R. Ac. Sci. clii. p. 913 (1911). 



