Phreatoicoides. 137 



coloured eggs. The lamellse are each subspherical in outline, 

 with margins entire. 



Sexual differences. — The only external differences in the form 

 of the female from the hymeneal male are that the first pereiopod, 

 which is similar to that of the normal male, has not the largely 

 developed clasping hand characteristic of the hymeneal form ; 

 there is no external male organ at the base of the seventh pair of 

 pereiopods, and no penial filament on the second pair of pleopods, 

 and when breeding there is a specially developed pouch. 



Generic position. — The nearest ally to the present species is 

 Phreatoiais australis, and, compared with that species, there is no 

 great difference in the head and pereion and their appendages, 

 except that in the present species the pereion is relatively much 

 more slender, but in the truncated telson it more nearly 

 resembles Phreatoicopsis terricola. The difference however in 

 the pleon, both in its relative length, which is short, and in the 

 pleura being unproduced, mark it off from either of the above 

 genera, and make it necessary to form a new one for its reception. 

 The measurement of a number of different individuals of the 

 present species showed an invariable degree of comparison 

 between the length of the pleon and telson to that of the cephalon 

 and pereion, and herewith I append the proportions of other 

 allied forms, which I measured from the drawings of Chilton, and 

 Spencer and Hall. Taking the ceplialon and pereion combined 

 as 100, then the pleon and telson combined measured in the 

 following species as under : — 



Phreatoicopsis gracilis - - - ^^ 



Phreatoicus australis - - - -^^ 



,, assimilis - - - jy^ 



typicus - - - - ^\ 



Phreatoicoides terricola - - - ^^^ 



