I'iMVlME — FOSSIL FISU KRO.M THR OLD ItED SANDSTONE. 
337 
including the tail-scgmont, is three feet nine inches, and it measures 
very nearly twelve inches across at its greatest breadth. Making a 
fair allowance for the head, the croatui'e naust have been over four 
and a- half feet long, and had thus formed a rather formidable 
lobster-like animal when swimming in the waters of the primeval 
woi'ld. It had not, however equalled in size the Pterygotus, to 
which three tail-segments, very recently found in a quarry in 
this immediate neighbourhood, had belonged, and which are now in 
my possession. 
I here give a rough sketch 
of tliis also very interesting 
fossil. The dotted line marks 
a portion which lifts clean 
out from the matrbc, leaving 
a very fine cast of what I 
consider to have been the 
dorsal plates of these seg- 
ments. The upper side of 
this fossil seems to have 
formed the upper portion 
of one of the layers or beds 
of the rock, and has the 
sculptnrings a good deal ob- 
literated ; these are, however, 
beautifully preserved on the 
under side, as also on the 
cast. These marking.s are 
much smaller on the caudal 
than on the other plates, in- ^ \y ^ 'WJ'll " & 
crea,sing in size, but stUl w v, \i Willi \. ^ S 
small, on the sub-caudal. 
The sub-caudal plate, and 
that anterior to it, have 
ridges along both the ven- 
tral and dorsal surfaces, dif- 
fering in this from some 
other specimens of these 
plates, which only show one 
ridge. The caudal segment is of some considerable thickness 
where it joins the one above it ; this rapidly narrows, until, after 
extending to about cne-fifth of its length, the upper and lower 
sides seem to join and become one plate. It would thus appear 
that the body of the creature had penetrated some little distance 
into this segment. No appearance of any vent or anal opening is 
found in these segments ; and as, from the state of preservation of 
this fossil, had such an opening existed, it would have been in all 
probability readily distinguishable, it affords strong negative evidence 
against the existence of the vent in this part of the body of the 
animal. The caudal plate is seven and a-half inches long by five 
VOL. nr. - u 
