Curton.—On some Subterranean Crustacea. 175 
The Isopod that I have to describe is remarkable from the fact that it 
has only six pairs of legs, whilst the normal number is seven pairs. In 
many Isopoda the young have at first only six pairs of legs, the last thoracic 
segment being but slightly developed and destitute of appendages,* and 
hence it might, at first sight, be thought that the animal I have is only an 
immature form. This, however, I think can hardly be the case, for there is 
nothing embryonic about the appearance of the animal, and moreover, I 
have examined altogether twenty-two specimens, varying in length from *16 
of an inch to -46 of an inch, and these all agree in wanting the last pair of 
thoracic legs. These specimens were obtained at various times from 
January up to October, 1881, and I think it is hardly possible that these 
can all be immature forms, and that during the whole time not one mature 
form should have been obtained. If it is, therefore, a mature form, the 
absence of the last pair of thoracic legs must I suppose be due to arrested 
development. 
ISOPODA. 
Cruregens, (nov. gen.) 
Generic characters:—Body sub-cylindrical. Head small. First six 
thoracic segments sub-equal, the seventh small and without appendages. 
Antenne sub-equal, neither having a flagellum. First pair of thoracic legs 
large and sub-chelate, the second and third sub-chelate but smaller, the 
three posterior pairs simple. First pair of abdominal appendages forming 
an operculum enclosing the branchial plates; last pair biramous. Telson 
Squamiform, 
Tn the antenne, the shape of the body and of the thoracic legs, this 
genus resembles Paranthura, Spence Bate, and in the shape of the telson 
and the last pair of abdominal appendages, it is like the closely allied genus 
Haliophasma, Haswell, but it differs from both in the absence of the last 
Pair of thoracic legs. 
Cruregens fontanus, sp. nov. Pl. X. figs. 1 to 12. 
Eyes none. Short blunt rostrum between the bases of the upper 
antenne. Upper antenne slightly shorter than the lower, formed of four 
joints ; first joint of lower antenne long, second short, third and fourth 
about as long as the first, the fourth being followed by a short terminal 
joint. First pair of thoracic limbs strong and sub-chelate; hand large, 
broadest at the proximal end, narrowing distally, che palm armed with 
stout spines, the finger strong and slightly curved ; the wrist about twice 
as long as broad. Last pair of abdominal appendages two-branched, first 
branch consisting of a single long narrow joint, the other of two joints, the 
Steal 
* “ Facts and Arguments for Darwin,” Fritz Miiller, pp. 70-72, 
