1886.] DURING THE VOYAGE OF H.M.S. ‘CHALLENGER.’ 113 
is represented by a single specimen, which was dredged in the Pacific 
Ocean at Station 218, in 1070 fathoms of water. It isa large 
Isopod, measuring upwards of two inches in length, and agrees in 
most particulars with such genera of the Cymothoide as Aga; but 
at the same time it presents certain remarkable peculiarities analo- 
gous to those exhibited by the aberrant genus Bathynomus lately 
described by Prof. A. Milne-Edwards from deep water in the North 
Atlantic. M. Milne-Edwards’s preliminary account of Bathynomus 
was communicated to the French Academy’, and a translation 
of his note has appeared in the Ann. & Mag. of Nat. Hist.? 
Apart from its huge size, the most remarkable feature in the 
organization of Bathynomus is the great development of branchial 
organs : ‘‘ it appears,” says M. Milne-Edwards, ‘‘ that the respiratory 
apparatus of an ordinary Isopod is insufficient to supply the physio- 
logical needs of Bathynomus, and that the development of special 
organs of a greater functional power has been rendered necessary. 
The abdominal limbs, which usually in this group constitute the 
sole branchial apparatus, in Bathynomus only serve the function of 
a covering to the gills which lie beneath them.” The gills of this 
Crustacean are in fact represented by a series of complicated branched 
outgrowths of the body-wall in the ventral region of the abdomen. 
The same end is attained by the Crustacean, which forms the sub- 
ject of the present remarks, in a different manner. Instead of a 
development of accessory respiratory organs, Anwropus (as I may term 
the genus from its chief structural peculiarity) exemplifies one 
extreme of the Isopodan type, in that all the abdominal appendages 
are converted into respiratory organs; the increase of respiratory 
surface is thus attained by an exaggeration of a structural character, 
which is common to all the members of the family, and which indeed 
is an important basis of distinction from other families of Crustacea. 
In all the members of this group more or fewer of the abdominal 
limbs are soft foliaceous appendages, which permit of an easy 
exchange of gases between the contained blood and the sea-water. 
There is no instance, however, among the Isopoda in which all the 
abdominal appendages are similar, functioning as respiratory organs, 
except in this deep-sea genus Anuropus. Bathynomus, as regards 
the uropoda, is quite a typical Isopod; these appendages form a 
pair of swimming-feet as they do in the other Cymothoide ®*. 
The modifications of the terminal pair of abdominal appendages or 
uropoda serve to divide the Isopoda into natural families, which 
prove to be allied in other particulars ; and some stress, therefore, 
from a classificatory point of view, should perhaps be laid upon the 
fact of their modification in Anuropus, though it is always open to 
question how far a purely adaptive character is of value. Since the 
present genus agrees with the Cymothoide in the general form of 
the body, in the number of free abdominal segments, and in fact in 
all essentials, it would perhaps be hardly permissible to remove it 
1 ‘Comptes Rendus,’ Jan. 1879. 
? Ann. & Mag. Nat. Hist. 1879 (vol. iii.), p. 241.. 
® There is a figure of Bathynomus in an interesting work recently published 
by M. Filbol and entitled ‘La vie au fond des mers,’ Paris, 1885. 
Proc. Zoou. Soc.—1886, No. VIII. 
