2 8 THE APPENDAGES., ANATOMY, AND RELATIONS OF TRILOBITES. 
The interpretation of the appendages of the cephalon is somewhat difficult. At the 
left of the glabella there are two large exopodites, the anterior of which lies over and par- 
tially conceals the other. These show by their position that they belong to the fourth and 
fifth cephalic appendages. In front of these lie two appendages which may be either endop- 
odites or exopodites, but which I am inclined to refer to the latter. Both are narrow and 
shaped like endopodites, but bear on their outer edges close-set fine setae. They also show 
what might be considered as faint traces of segmentation. If the first of these ran under 
the end of the exopodite behind it, as shown in Walcott's figure (pi. 22), then it would 
be necessary to interpret it as an endopodite, but it really continues down between the exop- 
odite and the glabella, and seems to be attached opposite the middle of the eye. The 
specimen does not indicate clearly whether this appendage is above or below the exopo- 
dite behind it, but one's impression is that it is above, in which case it also must be an 
exopodite. The appendage in front, being similar, is similarly interpreted. If this be cor- 
rect, then the exopodites of the second and third cephalic appendages are much shorter and 
narrower than those of the fourth and fifth. All of these appendages are obviously out of 
position, for the cheek has been pushed forward away from the thorax, though still pivot- 
ing on its inner angle at the neck-ring, till the eye has been brought up to the dorsal fur- 
row. In this way the anterior exopodites have been thrust under the glabella and all the 
appendages have been moved to the right of their original position. The anterior exopo- 
dite is very poorly shown, but seems to be articulated in front of the eye. The posterior 
exopodites are very similar to those on the thorax. The distal lobe is shown only by the 
second from the last. It has the same form as the distal lobes on the thoracic exopodites, 
and like them has much finer seta; than the main lobe, but it does not stand at so great an 
angle with the axis of the main lobe, nor yet is it so straight as shown in Walcott's 
figure. 
Measurements: The specimen is about 72 mm. long and 54 mm. wide at the genal 
angles. The pygidium is 22 mm. long and 37 mm. wide. The doublure is 1.5 mm. wide. 
The exopodite of the third thoracic segment is 19.5 mm. long. The pleural lobe at this point 
is 13 mm. wide without the spines and 18.5 mm. wide with them. The third exopodite of 
the cephalon was apparently about 15 mm. long when complete. 
Specimen No. 65515. 
Illustrated: Walcott, Sraithson. Misc. Coll., vol. 6y, 1918, pi. 20, figs. 3, 4. 
This is a small piece of the axial portion of a badly crushed Ncolenus, showing appen- 
dages on the left side as viewed from above. On the posterior half there are three large 
appendages which have the exact form of the exopodites of other specimens. There is a 
broad, oval, proximal lobe and a distal one at an angle with it. The proximal part of the 
shaft has fine setae or the bases of them, and the distal lobe faint traces of much finer ones. 
The form, and the setae so far as they are preserved, are exactly like those of the exopodites 
on the specimens previously described. (See fig. 4, page 26.) Beneath them there are 
slender, poorly preserved endopodites. 
In front of the exopodites and endopodites lie a series of structures which Walcott 
has called exites, but for which I can see another explanation. Walcott has shown them 
as four broad rounded lobes, but his figure must be looked upon as a drawing and not as a 
photograph, for it has been very much retouched. 
