74 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



Coxopodites. 



The primary function of the endobases of the coxopodites was doubtless the gathering, 

 preparation, and carrying of food to the mouth. Although the endobases of opposite sides 

 could not in all cases meet one another, they were probably spinose or setiferous and could 

 readily pass food from any part of the axial groove forward to the mouth, and also send 

 it in currents of water. The endobases of the cephalic coxopodites were probably modified 

 as gnathites in all cases, but little is known of them except in Triarthrus, where they were 

 flattened and worked over one another so as to make excellent shears for slicing up food, 

 either animal or vegetable. In some cases the proximal ends of opposed gnathites were 

 toothed so as to act as jaws, but a great deal still remains to be learned about the oral 

 organs of all species. 



The writer has suggested (1910, p. 131) that a secondary function of the endobases 

 of the thorax of Isotelus and probably other trilobites with wide axial lobes was that of loco- 

 motion. In Isotehis the endobases of the thorax are greatly over-developed, each being much 

 stouter and nearly as long as the corresponding endopodite, and the explanation seemed to 

 me to lie in the locomotor or crawling use of these organs instead of the endopodites. Cer- 

 tain trails which I figured seemed to support this view. 



POSITION OF THE APPENDAGES IN LIFE. 



In almost all the specimens so far recovered the appendages are either flattened by 

 pressure or lie with their flat surfaces in or very near the plane of stratification of the sedi- 

 ment. This flattening is extreme in Neolcnus, Ptychoparia, and Kootenia, moderate in Triar- 

 thrus and Cryptolithus, and apparently slight or not effective in Isotelus, Ceraurus, and 

 Calymcne. These last are, however, from the conditions of preservation, least available 

 for study. 



In Part IV, attention is called to a specimen of Triarthrus (No. 222) in which some 

 of the endopodites are imbedded nearly at right angles to the stratification of the shale. 

 This specimen is especially valuable because it shows that the appendages in the average 

 specimen of Triarthrus have suffered very little compression, and it also suggests the prob- 

 able position of the endopodites when used for crawling. 



In considering the position of the appendages in life, one must always remember one 

 great outstanding feature of trilobites, the thinness and flexibility of the ventral membrane. 

 The appendages were not inserted in any rigid test but were held only by muscular and con- 

 nective tissue. Hence we must premise for them great freedom of motion, and also rela- 

 tively little power. The rigid appendifers, and the supporting apodemes discovered by 

 Beecher, supplied fulcra against which they could push, but their attachment to these was 

 rather loose. 



Considering, first, the position of the appendages in crawling, it appears that different 

 trilobites used their appendages in different ways. Neolcnus had compact stocky legs, which 

 allowed little play of one segment on another, as is shown by the wide joints at right angles 

 to the axis of the segment. Such limbs were stiff enough to support the body when the 

 animal was crawling beneath the water, where of course it weighed but little. That such a 

 crawling attitude was adopted by trilobites has been shown by Walcott in his explanation 

 of the trails known as Protichnites (1912 B, p. 278). Many trilobites probably crawled in 



