166 C. E. JBeecher — Ventral Integument of Trilobites. 



finding a central groove, with two oblique grooves on each 

 side. These he considered as representing the cavities left by 

 the removal of the test from the basal joints of the legs, which 

 thus must have been attached along the median line of the 

 sternum. The supposed joints of the legs were filled with 

 rock, and his attempts to separate them from the matrix 

 resulted in failure. 



In the oral region, there were still more indefinite and 

 obscure evidences of cavities left by the removal of some ven- 

 tral testaceous structure. 



These meager remains in the rachis of the thoracic and oral 

 regions have furnished data for what must be considered as 

 the most remarkable and erroneous reconstruction of the trilo- 

 hite appendages and anatomy that has appeared since the time 

 of Burmeister, 7 in 1843. The latter, in the absence of any 

 material, confessedly based his opinions of the ventral anatomy 

 wholly upon theoretical considerations. JSTot only has Jaekel 

 to a large degree set aside the evidence presented by many 

 scores of specimens of Triarthrus, as described by the writer, 

 in which each detail of structure can be verified indefinitely, 

 but has also overlooked that afforded by the material illustrated 

 by Walcott, 10 Billings, 6 Mickleborough, 9 and Woodward. 12 

 Moreover, this single specimen of Ptychoparia has led its 

 describer to reconsider on a false premise the entire question 

 of the anatomy, ontogeny, phylogeny, and affinities of the 

 trilobite. 



It is the purpose of the present article to show that numer- 

 ous individuals of Triarthrus, as well as some material repre- 

 senting other genera, preserve evidence of what seems to be the 

 same structures as those described by Jaekel in Ptychoparia, 

 and also present indisputable testimony as to their correct 

 nature. It will be demonstrated that they do not belong in any 

 way to the appendicular system of the trilobites, but are really 

 the buttresses and apodemes of the ventral body integument. 



The marvelous state of preservation of many of the speci- 

 mens of Triarthrus, whose appendages have been studied by 

 the writer, affords very satisfactory indications, not only of the 

 presence of a ventral integument, but also of some of its 

 detailed characters. Jaekel states that in his opinion the 

 tmfavorable (" ungunstigen ") preservation of Triarthrus has 

 obscured the proximal structure of the legs, so that what he 

 calls the three basal joints are equivalent to the single un jointed 

 gnathobase of the coxopodite, as described by the writer. Inas- 

 much as Jaekel has never seen the original specimens described, 

 his statement is practically without foundation. It may also 

 be added that the types and best-preserved individuals have been 





