NEOLENUS. 23 



sides must have almost met on the median line. The segments of the endopodites are mostly 

 but little, if any, longer than broad, and at the distal end each shows two or more spines. 

 The propodite and dactylopodite are notably more slender than the others. The exopodites 

 of the thorax are broad and flat, and each shaft has two distinct parts with different kinds 

 of setie. The posterior edge of the proximal lobe is fringed with a slender, flat, overlapping 

 hairs which are a little longer than the width of the lobe, and stand at an angle of about 

 60 degrees with the direction of the axis of the appendage. The outer lobe is at an angle 

 with the main one, and has short, very fine setae oh the margin. One or two specimens show 

 some evidence of a joint between the inner and outer lobes, but in the great majority of 

 cases they seem to be continuous; if originally in two segments, they have become firmly 

 united. The exopodites of the thorax, like those of the cephalon, are directed diagonally 

 forward and outward. (PI. 21, fig. 6; pi. 22.) 



Pygidium. 



The pygidium of Neolcnus serratus is large, and usually shows five rings on the axial 

 lobe and four pairs of ribs on the sides. There are five pairs of biramous appendages be- 

 longing to this shield, and behind these a pair of jointed cerci. That the number of abdomi- 

 nal appendages should correspond to the number of divisions of the axial lobe rather than 

 to the number of ribs on the pleural lobes is of interest, and in accord with other trilobites, 

 as first shown by Beecher. 



The endopodites of the pygidium have the same form as those of the thorax, are long, 

 and very much less modified than those of any other trilobite whose appendages are known. 

 On some specimens, they extend out far beyond the dorsal test, so that nearly all the seg- 

 ments are visible (pi. 17, fig. 3; pi. 18; pi. 19; pi. 20, fig. i), but in these cases are prob- 

 ably displaced. The segments are short and wide, the whole endopodite tapering gradually 

 outward. The dactylopodite bears terminal spines, and the individual segments also have 

 outward -directed spines. 



The cerci appear to have been long, slender, very spinose organs much like the anten- 

 nules, but stiff rather than flexible. They are a little longer than the pygidium (pi. 17, figs, 

 i, 2), and seem to be attached to a plate on the under surface of the posterior end and in 

 front of the very narrow doublure. The precise form of this attachment can not be deter- 

 mined from the published figures. They bear numerous fine spines (pi. 17, fig. 3). 



Epipodites and Exiles. 



Doctor Walcott has found on several specimens of Neolenns remains of organs which 

 he interprets as epipodites and exites attached to the coxopodites. A study of the specimens 

 has, however, convinced me that both the large and small epipodites are really exopodites, 

 and that the exites are badly preserved and displaced coxopodites. Detailed explanation of 

 this interpretation is given below in the description of the several specimens involved. 



Description of Individual Specimens. 



Doctor Walcott was kind enough to send me eight of the more important specimens 

 of Neolenus figured by him, and since my interpretation of them does not agree in all re- 

 spects with his, I have thought it fairer to the reader to present here rather full notes 

 explaining the position I have taken. I understand that since I communicated my interpre- 

 tation of the epipodites and exites to him, Doctor Walcott has submitted the specimens to 



