Phreatoicoides. 123 



Phreatoicopsis, Spencer and Hall/ I propose the name of 

 Phreatoicoides. 



A striking feature about it is that, although inhabiting surface 

 waters, it is blind ; and on examining serial sections through the 

 head and brain, I failed to find any definite optic lobes, such as 

 occur in Phreatoicopsis terricoia, which I prepared for comparison. 

 This points to its near ancestors inhabiting caves or subterranean 

 waters. The New Zealand forms Phreatoiais typiais and P. 

 assimi/is, from subterranean waters, are blind ; P. australis and 

 P. terricoia., both inhabiting surface waters, have functioning eyes, 

 the former is recorded from Mount Kosciusko, N. S. W., near the 

 north-eastern border of Victoria, at an elevation of 6,000ft. and 

 the latter from forest country near Colac, in the western district 

 of Victoria. The species under review is from the eastern district 

 of Victoria.^ 



Another noteworthy characteristic of this species is the 

 apparent dimorphism in the males. The only outward differ- 

 ence that I have observed is in the ultimate and penultimate 

 joints of the first pereiopods, which together act as a clasping 

 "hand." The two forms are shown in Figs. 9 and 10. In the 

 one form it is similar to that of all females, but in the other the 

 propodos is very much larger, and the dactylos longer and more 

 curved, showing the peculiarity of the males of the hitherto 

 described species of Phreatoicus and Phreatoicopsis. The two 

 forms of males noted in the present species are evidently not due 

 to maturity alone, for in Fig. 9 which was drawn from a male of 

 17 mm. in length, the normal form is shown, whereas in Fig. 10, 

 the male measured only 9 n>m. long, and shows the sexual 

 differentiation in the enlarged propodos as described by Chilton, 

 and Spencer and Hall. And further, amongst a considerable 

 number collected I only found three males with the enlarged 

 propodos, none of which were longer than 1*2 mm. It seems 

 reasonable therefore to con.sider that in this species mature males 

 exist in two forms. 



It is well known that an apparent dimorphism exists \\\ some 

 few widely separate orders of Crustacea, but whether permanent, 



1 Proc. Roy. Soc. Victoria, vol. ix. p. 12. 



'•2 Since writing the above I find that Mr. J. M. Thomson has recorded P. auxtralis from 

 pools on Mount Wellington (4,000ft.), Tasmania. Proc. Royal .Soc. Tasmania for 1892, p. 76. 



