RECENT VIEWS ON THE TRILOBITES. 207 
was thin and delicate, and was strengthened in each segment by 
a transverse arch, to which the appendages were attached, being 
thus something like the ventral membrane of the abdomen of a 
cray-fish. The intestinal canal had previously been discovered 
by Professor Beyrich. Mr. Walcott says it is a very rare thing 
to find traces of it, one in a hundred being a large proportion. 
From the mouth it extends forward a little, and then curves 
backward, proceeding direct to the pygidium. The mouth opens 
obliquely backward instead of directly downward, and is formed 
of four pairs of appendages, which have a general structure like 
the cephalic legs of Lzmulus and Eurypterus. The basal joints 
of these legs were large, and were undoubtedly used as jaws as 
in the American king-crab (Lzmulus). Each leg probably con- 
sisted of six or seven joints ; but as no one leg was seen entire, 
this is somewhat doubtful. In the first three cephalic appen- 
dages, all the joints except the first were slender; but in the 
fourth the terminal joints were expanded so as to form a 
swimming leg. Of the appendages of the body there appear 
to have been one pair of legs to each segment, both of the thorax 
and the pygidium. They were slender, each consisting of six or 
seven joints, of which the basal one was the largest, and sup- 
ported a branchia and an epipodite, which consisted of two or 
more joints, and was probably kept in constant motion so as to 
produce a current of water circulating among the branchiez. The 
branchiz themselves were of three forms. In the first they 
bifurcate near the base, and extend downwards and outwards as 
two simple slender tubes or ribbon-like filaments; the second 
kind are similar to these, but have the two branches spiral ; the 
third form appears to be confined to the anterior segments of 
the thorax, they consist of several straight filaments, radiating 
from a central support. Possibly those parts that are still pre- 
served do not represent the actual branchie, but supports to 
which the delicate branchiz were attached. 
These are the conclusions that Mr. Walcott feels justified 
in forming ; whether they will all be confirmed or not remains 
to be seen. Some of them are evidently most fully supported by 
his sections, of which he gives drawings, to all appearances very 
accurate ; but with regard to others the evidence can hardly be 
considered quite satisfactory. This is more particularly the case 
with the appendages. These, he says, wereambulatory ; and yet 
at the same time he says that their integument was very thin, in 
this being in marked contrast to the thick dorsal shell. It was, 
in fact, so thin that he has to produce evidence to show that it 
could be preserved sufficiently well to be observed in the fossil 
state, and cites the case of the gill feet of ranchipus being pre- 
served inthe Eocene fresh-water strata on the Isle of Wight. 
Now, if the membrane of the legs were as delicate as this, they 
could not have been of much use as ambulatory organs ; while 
from their slender form (with the exception of the fourth cephalic 
appendage) they would have been almost useless as swimming 
organs. : 
