76 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



is as yet known of the musculature. The coxopodites of course had less freedom of move- 

 ment in this respect, and probably could not turn their faces. For this reason, it seems to 

 me likely that those coxopodites which are compressed did not stand with their flattened 

 faces vertical, but in a position which was nearly horizontal or at least not more than 45 

 from the horizontal. If the flattened faces were vertical, they would be in constant oppo- 

 sition to the water during forward movements and would be of no use in setting up cur- 

 rents of water toward the mouth, as every back stroke would reverse the motion. 



The position of the exopodites in life seems to have been rather uniform in all the 

 genera now known. I have set forth on a previous page my reasons for thinking that they 

 took little part in swimming, and I look upon them as being, in effect, leaf-gills. It seems 

 probable that in all genera the exopodites were held rather close to the test, the shaft more 

 or less rigid, the filamentous setae gracefully pendent, but pendent as a sheet and not individ- 

 ually, there having been some method by which adjoining setae were connected laterally. 

 Free contact with the water was thus obtained without the mingling of endopodites and ex- 

 opodites which would have been so disastrous to progression. 



