42 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



specimens of Triarthrus and Cryptolithus he did not again publish upon the subject of 

 appendages until forced to do so by the doubts cast by Jaekel (1901) upon the validity of 

 his earlier conclusions. Because of certain structures which he thought he had interpreted 

 correctly from a poorly preserved specimen of Ptychoparia, Jaekel came to the conclusion 

 that Beecher's material was not well preserved. Professor Beecher would have taken much 

 more kindly to aspersions upon his opinions than to any slight upon his beloved trilobites, 

 and his article on the "Ventral Integument of Trilobites" of 1902 was designed not only 

 as an answer to Jaekel, but also to show by means of photographs the unusually perfect 

 state of preservation of the specimens of Triarthrus. This article, like so many describ- 

 ing the appendages of trilobites, beginning with Matthew's, was published in two places 

 (Beecher 1902). 



Most of Beecher's papers, except the last one, were reprinted in the volume entitled 

 "Studies in Evolution," published by Charles Scribner's Sons at the time of the Yale Bi- 

 centennial in 1901. The part pertaining particularly to Triarthrus is on pages 197 to 219. 



Moberg (1907), in connection with a specimen of Eurycare angustatum which he thought 

 preserved some appendages, described and illustrated some of the appendages of Triarthrus. 



The most recent discussion of Triarthrus, with some new figures, is by Walcott (1918, 

 p. 135, pis. 29, 30). He gives a summary of Beecher's work with numerous quotations. 

 The principal original contribution is a discussion of the form and shape of the appendages 

 before they were flattened out in the shale. He found also what he thought might possibly 

 be the remains of epipodites on three specimens, one of which he illustrated with a photo- 

 graph. I have seen nothing which could be interpreted as such an organ in the many speci- 

 mens I have studied. 



A point in which Walcott differs from Beecher in the interpretation of specimens is 

 in regard to the development of the endopodites of small pygidia. Beecher (1894 B, pi. 

 7, fig. 3) illustrated a series of endopodites which he likened to the enclites of a thoracic 

 limb of Apus. Doctor Walcott finds that specimens in the United States National Museum 

 show slender endopodites all the way to the back of the pygidium, and thinks that Beecher 

 mistook a mass of terminal segments of exopodites for a series of endopodites. On care- 

 ful examination, however, the specimen shows, as Beecher indicated, a series of endopodites 

 in undisturbed condition (No. 222, our pi. 4, fig. 5). 



Restoration of Triarthrus. 



One of the more important points noted in the later studies of Triarthrus is that the 

 gnathites of the cephalic appendages are much less like the endobases under the thorax than 

 Beecher earlier thought, and showed in his restored figures and in his model. The four 

 gnathites of each side are curved, flattened, not club-shaped, and so wide and so close together 

 that they overlap one another. The metastoma is somewhat larger and more nearly cir- 

 cular than Beecher's earlier preparations led him to suppose. 



The restoration here presented is modified only slightly from the one designed by Pro- 

 fessor Beecher, and the modifications are taken principally from figures published by him. 

 The gnathites are drawn in form more like that shown by the specimens and his figures in 

 the American Geologist (1895 A), and the metastoma is taken from one of the specimens. 

 On the thorax the chief modification is in the addition of a considerable number of spines 

 to the endopodites. In spite of the trivial character of most of these changes, they empha- 



