NO. 5 CAMBRIAN TRILOBITES 3O9 



(ocular) ridge crossing fixed cheek. Thorax with 7 to ii segments ; 

 pleural furrows broad and usually straight. Pygidium more or less 

 strongly ribbed. Surface of test apparently punctate and with irregu- 

 lar, inosculating, fine, sharp ridges which may be smooth or broken up 

 into granulated ridges. 



The typical genus of this family is Corynexochiis, and of the 

 subfamily Dolichometopinse the typical genera are Bathyuriscus and 

 Dolichometopus. Corynexochiis and Bathyuriscus originate in the 

 upper portion of the Lower Cambrian. Corynexochiis has four 

 Lower and five Middle Cambrian species. Its subgenus Bonnia is 

 confined to the Lower Cambrian, as far as known. Dolichometopus 

 with its large cephalon and pygidium has 13 Middle Cambrian spe- 

 cies. Bathyuriscus has two species in the upper portion of the Lower 

 Cambrian, B. bat is and B. primus, and twenty species in the Middle 

 Cambrian. The line of descent indicated in Cambrian time is from 

 a Cory)iexochns-likQ ancestor to Bathyuriscus and Dolichometopus. 



The pleural lobes of the pygidium of young specimens of Dolicho- 

 metopus are ribbed as in Corynexochiis, and thus suggest that the 

 genus descended from a Corynexochus-like ancestor. The glabella 

 and eyes of some forms of Dolichometopus approach some species 

 of Olenoides. 



The thoracic pleural segments of Corynexochiis are often similar 

 in character to those of Dorypyge, and there is also a resemblance in 

 the glabella of some of the species of the subgenus Bonnia. 



Genus Corynexochiis Angelin. — Cephalon larger than the py- 

 gidium. Glabella expanded anteriorly and with glabellar furrows. 



Subgenus Bonnia. — Glabella with sides subparallel and with slight 

 traces of glabellar furrows. 



Subfamily Dolichometopinse. — Corynexochidae with glabella ex- 

 panded in front or with subparallel sides. 



Genus Dolichometopus Angelin. — Cephalon and pygidium subequal 

 in size. Glabella nearly smooth. 



Genus Bathyuriscus Meek. — Cephalon usually larger than py- 

 gidium. Glabella with distinct furrows. 



Genus CORYNEXOCHUS Angelin 



Corynexochus Angelin, [1852] 1854, [1878] Pal. Scandinavica, 2d ed., 1854, 



p. 59. (Latin diagnosis of genus. First species, C. spinulosus, p. 59, 



pi. 2Z, figs. 9, ga, 11?.) 

 Corynexochus Zittel, 1885, Handbuch d. Pal., Vol. 2, Munich, p. 602. (Brief 



diagnosis of genus.) 

 Karlia Walcott, 1889, Proc. U. S. Nat. Mus. for 1888, Vol. 11, p. 444. (Genus 



described.) 



