248 T. H. Clark — New Trilobite Appendage. 



In the Asaphidae, no exopodites are definitely known, but 

 the endopodites are long*, although slender. In Triar- 

 thrus, the basipodites, ischiopodites and meropodites are 

 for the most part much modified in form, but in any case 

 the endopodites are as long as, if not longer than, the 

 exopodites. In the form of the exopodite alone, some 

 comparison might be made between the present specimen 

 and Walcott's figured specimen of Ptychoparia cordil- 

 lerae Rominger. 1 In all other trilobites the exopodites 

 are no longer than the endopodites. Thus, off anatomical 

 grounds alone, it would be impossible to connect this form 

 with any trilobite whose appendages are known. Of the 

 genera represented in the Shumardia zone only Isotelus 

 and Triarthrus have so far yielded recognizable appen- 

 dages. The most abundant trilobite is Shumardia granu- 

 losa Billings, which outnumbers all others about five to 

 one ; but this species is much too small to have possessed 

 the appendage in question. The remaining genera repre- 

 sented in the Shumardia limestone are Agnostus, Endym- 

 ionia, Symphysurus, Telephus, and Holometopus, to any 

 one of which this appendage might belong. There seems 

 to be no evidence for placing it within any particular one 

 of these genera. 



Museum of Comparative Zoology, 

 Cambridge, Mass. 



1 Smithson. Misc. Coll., vol. 67, pi. 21, figs. 3-5, 1918. 



