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, Cryptolitlms, Ncolcnus, 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. 



