LOWER CARBONIFEROUS ROCKS OF ESKDALE AND LIDDESDALE. 79 
longer, the sixth being the longest. The four posterior segments are orna- 
mented by a broad marginal band anteriorly, which sends back an occasional 
buttress which is soon lost in the test, except in the case of the median one on 
the three last segments, which is continued to their posterior margins. Those 
in a line with the mesial and the two main lateral crests of the carapace are 
larger and more pronounced than the rest, and are continued down into the 
telson. As they approach that organ they become ornamented with occasional 
spines which gradually increase in size backwards. All the abdominal seg- 
ments have large pleure pointed backwards. The appendages on the first five 
segments have not been observed. Those on the sixth consist of a broad joint 
articulated with it at the posterior angle on each side, each of which supports 
a pair of broad swimming flaps. That corresponding to the exopodite is 
strengthened by a strong, narrow, knife-blade-like rachis on its exterior margin. 
Its inner margin is supported by a conical spine which is directed towards the 
point of the knife-blade portion. The inferior and inner margins are broadened 
out into a flap, which is further strengthened by corrugations of the test. The 
endopodite is composed of a fin-like lobe with a central slender spine-like 
thickening, and is corrugated near the margins. The telson, which is broad at 
the base, tapers rapidly and increasingly for about half its length, whence it is 
continued into a long sharp spine and looks like the section of a boy’s peg-top. 
At the angles made by what corresponds to the insertion of the peg, two pairs 
of short conical spines are articulated with it. The convexity of this species is 
slight, as it is invariably fossilised with its back upwards. 
Observations.—Besides the above external characters, the specimens in the 
Survey collection show several points in its anatomy. The eyes as seen, fig. 4a, 
seem to have been large, but they are so much crushed that their original form 
cannot be made out. Nothing can be said about the maxille or maxillipedes, 
though there is little doubt that the confusion in the carapaces of figs. 4a and 
4bis caused by their being crushed through it. Part of the confusion is, doubt- 
less, owing to the hard parts of the stomach and the endophragmal system. 
In fig. 4 the thoracic segments are seen shining through the carapace, and on 
one side the branchial arches are also distinguishable. In the abdominal seg- 
ments the sternal arches are seen to be pressed up through the tergum, fig. 4. 
Their epimera are almost as broad as the basis of the pleure, but the stern 
are very narrow, which shows that the segments to which these belong had a 
great deal of play. The tail is enormous compared with the size of the creature, 
and must have been a most effective organ for swimming backwards. As it is 
now found, in many cases the strengthening ridges only are preserved, as in 
figs. 4 and 4a, and these give to the creature a very formidable aspect. 
Fortunately other specimens, as in fig. 4c, show the true nature of them. 
The sharp knife-blade-like portion of the exopodite is ornamented on its 
