28 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 (kiter edges close-set fine sete. 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 setae 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, Smithson. Misc. Coll., vol. 67, 1918, pi. 20, figs. 3, 4. 



This is a small piece of the axial portion of a badly crushed Neolenus, 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 setje 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. 



