150 



THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



Recent 



Fig. 41. A diagram showing possible lines of descent of the other Arthropoda from the Trilobita. The 

 three recognized orders of the latter are shown separately. The known geological range is indicated in solid 

 black, the hypothetical range and connections stippled. The short branch beside the Opisthoparia represents 

 the range of the Haplopoda. The term Arachnida is used for all arachnids other than Merostomata, merely 

 as a convenient inclusive name for the groups not especially studied. 





