398 PROCEEDINGS OF THE ACADEMY OF [1894. 



2. The fingers of the chelae in the Acanthephyridce are normal in 

 shape, in the Atyidce they are provided with a peculiar pencil of 

 hairs. I may add that the habits of the two families are wholly 

 different, the Aca?ithephyridce being true marine animals, especially 

 abyssal, the Atyidce being true fresh- water forms. 



Among the Atyidce Kingsley distinguished two subfamilies, Aty- 

 ince and Ephyrince. Since, however, there are but a few genera in 

 this family, a subdivision is needless. The genera form a continu- 

 ous series, the transition being so gradual that it is difficult to define 

 the limits of the two subfamilies. In the following synopsis of the 

 genera the first three named, Xiphocaris, Troglocaris, and Atyaèphyra 

 may be regarded as belonging to the subfamily Ephyrince as created 

 by Kingsley, the others as belonging to the Atyince. Because the genus 

 Ephyra, from which is derived the name Ephyrince, is a synonym, 

 this subfamily must be renamed, and I propose to name it, if at all, 

 Xiphocarince. 



The presence of exopodites on the pereiopoda of the Xiphocarince, 

 the shape of the carpal and propodal joints of the first two pairs of 

 pereiopoda, and the shape of the rostrum constitute a very close re- 

 semblance to the Acanthephyridce. Atyaèphyra makes a transition to 

 the Atyince, bearing exopodites only on the first two pairs of pereio- 

 poda, and having the carpal joints of these legs excavated at the distal 

 extremity. This excavation is very characteristic in the true Atyince, 

 but in Caridina the carpal joint only of the first pair of legs shows 

 this peculiarity, that of the second pair being normal. Atyoida is 

 intermediate between Caridina and Atya in the shape of the propo- 

 dal joints of these legs. Within the limits of Caridina occurs a 

 reduction of the form of the rostrum (being in the Xiphocarince 

 long and serrated), which in most species of Caridina is longer or 

 shorter and serrated, in a few very short and not serrated. In 

 Atyoida and Atya the rostrum is usually short, but now and then it 

 bears a few teeth on the inferior margin. Thus the series formed by 

 Xiphocaris, Atyaèphyra, Caridina, Atyoida, and Atya is a continuous 

 one, whilst the genus Troglocaris is closely allied to Xiphocaris 

 differing only by the rudimentary condition of the eyes, due to its 

 subterranean habits in cave-waters. 



The genus Atya is the most extreme of the family. The adult 

 males of the species of this genus attain a considerable size, and the 

 third pereiopoda undergo with increase of age a change in shape 



