249 THE ATLANTIC. [CHAP. Lv. 
of the back divide the cephalo-thorax into four areas, the two 
anterior indicating the hepatic, and the posterior the branchial, 
regions. 
The abdomen consists of six segments and the telson. A 
ridge runs along the dorsal surface of each segment in the mid- 
dle line, and rises on the first segment into one, and on the four 
succeeding segments into two spines, directed forward. As in 
W. leptodactyla, not only are the eyes and eye-stalks absent, but 
there is no indication of a space for their accommodation in the 
position in which eyes are normally developed. The antenne 
are placed one pair beneath the other. There is a lamellar ap- 
pendage, which scarcely rises to the top of its basal segment, at- 
tached to the outer antenna. The flagella of the outer antenne 
are 21 mm. in length, and the larger flagella of the inner an- 
tennee nearly equal them. The parts of the mouth are normal. 
Four pairs of the ambulatory legs bear delicate chele sparsely 
spined along the upper edge, and the fifth pair end in a simple 
curved process. The first pair of ambulatory legs are not so 
long in proportion to the body or so slender as in W. leptodac- 
tyla. The first abdominal feet are style-like, and flattened at 
the end. The swimmerets have three joints, to the first two of 
which the palpi are attached. The telson and the caudal ap- 
pendages are in no way remarkable. They, with the palpi of 
the swimmerets, the basal joints of the ambulatory legs, and the 
basal joints of the antennee, are fringed with fine hairs. 
Willemoesia crucifer certainly differs widely in general ap- 
pearance from the recent Astacidee, at the end of which family 
we should, however, be inclined to place it for the present. It 
has a very close resemblance to some fossil forms, particularly 
to the various species of the genus Hryon. It has been already 
remarked that Wallemoesta in its flattened cephalo-thorax ap- 
proaches the Palinuridge: in all the living members of that fam- 
ily, however, the first pair of legs are monodactylous, while 
in Willemoesia they are didactylous. The fossil genus Hryon 
