PART I. 
THE APPENDAGES OF TRILOBITES. 
Terminology. 
The terminology employed in the succeeding pages is essentially the same as that used 
by Beecher, with two new terms added. Beecher assigned to the various segments of the 
limbs the names suggested by Huxley, but sometimes used the name protopodite instead of 
coxopodite for the proximal one. It is obvious that he did not use protopodite in the cor- 
rect sense, as indicating a segment formed by the fusion of the coxopodite and basipodite. 
The usage employed here is shown in figure i. 
Fig. i. — Triarthrus becki Green. Diagram of 
one of the limbs of the thorax, viewed from 
above, with the endopodite in advance of the exo- 
podite. i, coxopodite, the inner extension being 
the endobase (gnathobase on cephalon) ; 2, basip- 
odite, springing from the coxopodite, and sup- 
porting the exopodite, which also rests upon the 
coxopodite ; 3, ischiopodite ; 4, meropodite ; 5, 
carpopodite ; 6, propodite ; 7, dactylopodite, with 
terminal spines. 
The investigation of Ceraurus showed that the appendages were supported by processes 
extending downward from the dorsal test, and on comparison with other trilobites it appeared 
that the same was true in Calymene, Cryptolithus, Neolenus, and other genera. Thin sec- 
tions showed that these processes were formed by invagination of the test beneath the dorsal 
and glabellar furrows. While these processes are entirely homologous with the entopo- 
physes of Limulus, I have chosen to apply the name appendifcr to them in the trilobites. 
The only other new term employed is the substitution of endobase for gnathobase in 
speaking of the inner prolongation of a coxopodite of the trunk region. The term gnatho- 
base implies a function which can not in all cases be proved. 
The individual portions of which the limbs are made up are called segments, and the 
articulations between them, joints. Such a procedure is unusual, but promotes clearness. 
