396 NORTH AMERICAN INDEX FOSSILS. 



Subfamily Catometopa Milne-Edwards. 

 XXV. Plagiolophus Bell. 



Cephalothorax small, transversely ovate-quadrangular, broader 

 than long ; anterior border curved, slightly rostrate, not dentate and 

 with median longitudinal *furrow ; orbits deep and wide ; regions 

 of the cephalothorax outlined by deep furrows, arched and granu- 

 losa The four ambulatory legs are similar to one another. Cre- 

 tacic-Eocenic. 



45. P. vancouverensis Woodward. Cretacic. 

 Frontal border straight ; rostrum bifid, with two small elevations 



divided by a groove; lateral borders gently rounded; posterior 

 border nearly straight; lobes of carapace marked, forming three 

 transverse lines across the carapace. (Hind feet unknown, and 

 generic reference provisional.) 



Nanaimo of Vancouver Islands, B. C. 



XXVI. Arch^opus Rathbun. 



Differs from Plagiolophus in having the last pair of thoracic 

 legs very small, and the orbits much deeper and wider. Cretacic. 



46. A. antennatum Rathbun. Cretacic. 

 Differs from P. vancouverensis in its slender acuminate, non- 

 bifid and obliquely-inclined rostrum, and in having each orbit occu- 

 pying about one fourth of the anterior border of the carapace, 

 with a prominent outer, and fainter inner triangular tooth or spine 

 on the dorsal border, and one each on the inner ventral border of 

 the orbit. The carapace is about one and three fifths times as 

 broad as long; antero-lateral margins straight and converging 

 forwards, with five unequal and irregularly disposed tubercles; 

 postero-lateral margins rounded to the bilobed hinder end ; cervical 

 sulcus well-developed, cardiac and branchial regions with trans- 

 verse ridges; central depressions of carapace form a broad H. 

 CheHpeds (of female) of moderate size, subequal, with thick 

 merus and narrow, strongly arcuate chelae, the fingers somewhat 

 longer than the palm, very slender, grooved, opposed edges meet- 

 ing and finely dentate. 



Chico of San Mateo County, Cal. 



