124 Proceedings of the Royal Society of Victoria. 



or only changing upon the casting of the skin previously to the 

 breeding season and afterwards alternating back again at the 

 next moult, was not known until Faxon kept alive and bred in 

 confinement the fresh-water cray-fish of the United States, 

 Cambariis rusficans, Gerard, when he found that the two stages 

 are not permanent " but simply alternating periods in the life of 

 the individual, the ' first form ' (so called by Dr. Hagan) being 

 assumed during the pairing season, the ' second form,' during the 

 intervals between the pairing season."^ 



I consider it probable that in the species now under considera- 

 tion a similar alternation in the males takes place, and 1 shall 

 describe the structure of the two forms later under the head of 

 Normal and Hymeneal. 



Living in the same water as the present species were large 

 numbers of an Amphipod, which, upon superficial examination, 

 appears to be a closely akin genus to Gammarus. Also, from a 

 little pool within a few yards from the streamlet, I took another 

 Amphipod, possibly a Niphargus, and a small Isopod, of the 

 family Asellidce. These I hope to determine later. 



In the following description I have adhered as closely as 

 possible to the arrangement and nomenclature of Chilton, and 

 Spencer and Hall. 



Phreatoicoides, n.g. 



Body linear, subcylindrical. Upper antennte short, lower long, 

 with flagellum. ]\landibles with an appendage. First pair of 

 legs suhchelate, others simple. The legs are divided into an 

 anterior series of four and a posterior series of three. Pleon 

 short, slightly laterally compressed, of six distinct segments, last 

 joined to telson. Pleopoda exposed, foliaceous. Uropoda 

 birainous, styliform. Telson large, sharply truncate. 



Phreatoicoides gracilis, n. sp. 



Specific diagnosis. — Body slender, greatly elongated, long 

 flexuose setai scattered sparsely over surface. Pleura of pleon not 

 produced, their inferior margins sparsely fringed with small 



1 Faxon, " On the so called Dimorphism in the genus Cambarus." American Journal of 

 Science, vol. xxvii, 1884. 



