Subclass Xenopoda nov.
Crustacea with more or less eurypterid-like form, one pair of uniramous antennæ, 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 segments and a telson. Cephalic appendages grouped about the mouth.
Family Sidneyidæ 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. Middle Cambrian, British Columbia.
Genus Amiella Walcott.
Middle Cambrian, British Columbia.