480 PROCEEDINGS OF THE GEOLOGICAL £0CIETY. [May 11, 
from the space between the two lobes of the hypostoma, where we 
must suppose the mouth to be situated, backwards along the median 
line to the pygidium. This corresponds in position to the sternum 
of the ordinary crustacea. ‘The legs are arranged in eight pairs, the 
bases of each pair being situated exactly under one of the eight seg- 
ments of the thorax, and at the sides of the sternal groove. 
The legs of the first, pair are better-preserved than the others. 
They curve forwards and can be traced to a point nearly under the 
outer edge of the eye, or, rather, between the eye and the outside of 
the head. The other seven pairs follow at the average distance of 
two and a half lines from each other. The eight pairs thus occupy 
about twenty lines of the Icngth of the ventral surface. ‘This is 
exactly the length of the thorax, measured on the upperside. ‘This 
trilobite has always eight segments in the thorax ; and thereis thus 
on the underside one pair of appendages to each segment. Although 
some of them are very imperfect, and the portions that remain are 
somewhat displaced, with a little study of the specimen it can be 
seen that they all curve forwards, and are thus, most probably, am- 
bulatory rather than natatory legs. 
There appear to be several joints in each of these appendages; but 
the exact number cannot be made out. On the left side, the first 
four legs show very clearly that there are at least two, one at five 
lines from the side of the groove, and another about three lines fur- 
ther out. The pesition of each of these is indicated by a smail protu- 
berance (Pl. XX XI. fig.1,). On the right side the preserved portions 
of the legs are longer, and thus indicate a greater number of arti- 
culations, although they cannot be distinctly seen. I think that 
each leg consisted of at least four or five articulations. 
On the pygidium there are three small ovate tubercles, arranged 
in a line, that seem to be organic (fig. 1, d); and if they are so, they 
are, perhaps, the processes to which respiratory feet were attached. 
The length of the specimen is four and a half inches, and the 
width two and a half inches. On a side view the height of the 
head just behind the eyes is nine lines, and at the middle of the 
thorax about seven lines. The depth of the internal cavity at the 
back part of the head is seven lines, and at the last segment of the 
thorax four lines. The plane in which the legs are situated is 
therefore not so low down as the extremities of the pleure. The 
visceral cavity is thus about one-third less than the whole bulk of 
the animal (Pl. XX XIU. fig. 1). 
The above is all that I desire to say at present concerning this 
remarkable specimen. ‘The first and all-important point to be de- 
cided is, whether or not the forms exhibited on its underside are 
truly, what they appear to be, locomotive organs. If this question 
be decided in the affirmative, it will then remain for Carcinologists 
and others to homologize them with the limbs of existing crustacea. 
It is scarcely necessary to remark, in this place, that, in view of 
the great zoological questions that are at present being discussed, 
the correct determination of the affinitics of the Trilobites is of ex- 
traordinary importance. 
