Family Emeraldellidæ nov.
Trunk with biramous appendages in anterior part, and appendages on all segments except possibly the spine-like telson.
Genus Emeraldella Walcott.
Cephalic appendages simple spiniferous endopodites. Eyes unknown. Middle Cambrian, British Columbia.
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.