36 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOB1TES. 



The most conspicuous feature of this specimen is the presence of nine pairs of large 

 coxopodites behind the hypostoma, and of the remains of ten pairs of endopodites, mak- 

 ing in all ten pairs of appendages which are easily seen. The apportionment of these seg- 

 ments to cephalon, thorax, and pygidium is not agreed upon by the people who have 

 examined the specimens, but if one remembers that it is the outer and not the inner end 

 of the coxopodite which articulates with the appendifer, it at once becomes evident that 

 the first two pairs of appendages on the specimen are the last two pairs belonging to the 

 cephalon, and that the next eight pairs are those of the thorax. 



The impressions of fourteen pairs of coxopodites are readily counted on the pygidium, 

 and as Doctor Walcott noted sixteen pairs on the actual specimens, his number was prob- 

 ably correct. 



Cephalon. 



Projecting the line of the back of the cephalon through from the dorsal side, it is 

 found that the posterior tips of the hypostoma are 7 mm. in front of the posterior mar- 

 gin of the cephalon, and that the points of attachment of the posterior pair of cephalic ap- 

 pendages (the second pair shown on the specimen) are just within the posterior margin. 

 The gnathobases of this pair of appendages extend back some distance beneath the thorax, 

 and so give the impression that they belong to that part of the body. So far as can 

 be determined, the cephalic appendages do not differ in any way from those of the thorax. 

 On the mould of the ventral surface, just outside of the lateral edge of the right lobe of the 

 hypostoma, is the somewhat imperfectly shown impression of the endopodite of the third 

 cephalic appendage. The point of junction of the endopodite and coxopodite is about 2 mm. 

 in front of the tip of the adjacent branch of the hypostoma, and the gnathobase is curved 

 around just behind it. This accounts for three of the pairs of cephalic appendages. The 

 second cephalic appendages must have thrust their gnathobases under the prongs of the 

 hypostoma, and the endopodites were probably close to its edge. No trace of this pair ap- 

 pears on the specimen. 



Thorax. 



The thoracic appendages are the best preserved of any, and show the large coxopodites 

 and the more slender endopodites which do not extend to the outer margin of the test. 

 The latter extend forward and outward for about one half their length, then turn backward 

 in a graceful curve. 



Walcott's figure in Science shows hair-like markings on the under side of the right 

 half of the thorax. These were interpreted by both Walcott and Beecher as fringes of the 

 exopodites, but since the setas of those organs on all other trilobites are always above the 

 endopodites, while these are represented as below them, it would seem doubtful if this in- 

 terpretation can be sustained. Furthermore, I find no trace of them on either cast or mould, 

 and the actual specimen does not now show them. 



Pygidium. 



The coxopodites and endopodites of the pygidium seem to be similar to those on 

 the thorax, but both are shorter and more slender, and the former decrease in length 

 rapidly toward the posterior end. As mentioned above, it is not perfectly plain how many 

 appendages are present, but I have accepted Doctor Walcott's count of sixteen pairs. Of the 

 endopodites only the barest traces are seen, and of exopodites nothing. 



