SUMMARY. 149 
Family Marrellidfe Walcott. 
Cephalon with long genal and nuchal spines. Eyes marginal. A single species : Marrella 
splendens Walcott, Middle Cambrian, British Columbia. 
Order Aglaspina Walcott. 
Body trilobite-like, with few thoracic segments, and a spine-like telson. Appendages bira- 
mous. 
Family Aglaspida; Clarke. 
Cephalon trilobate, with or without compound eyes, seven or eight segments in the thorax 
Genus Aglaspis Hall. 
Compound eyes present, seven segments in thorax. Upper Cambrian, Wisconsin. 
Genus Molaria Walcott. 
Compound eyes absent, eight segments in thorax. Middle Cambrian, British Columbia. 
Genus Habelia Walcott. 
Compound eyes absent. Not yet fully described. Middle Cambrian, British Columbia. 
Subclass Xenopoda nov. 
Crustacea with more or less eurypterid-like form, one pair of uniramous antennae, biramous 
appendages on anterior part of trunk, modified endopodites on cephalon. 
Order Limulava Walcott. 
Cephalon with lateral or marginal eyes and large epistoma. Body with eleven free seg- 
ments and a telson. Cephalic appendages grouped about the mouth. 
Family Sidneyida? Walcott. 
Trunk probably with exopodites only, and without appendages on the last two segments. 
Telson with a pair of lateral swimmerets. 
Genus Sidneyia Walcott. 
Third cephalic appendage a large compound claw. Gnathobases forming strong jaws. Mid- 
dle Cambrian, British Columbia. 
Genus Amid la Walcott. 
Middle Cambrian, British Columbia. 
Family Emeraldellida? nov. 
Trunk with biramous appendages in anterior part, and appendages on all segments except 
possibly the spine-like telson. 
Genus Emcraldella Walcott. 
Cephalic appendages simple spiniferous endopodites. Eyes unknown. Middle Cambrian, 
British Columbia. 
