80 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



The facial suture diverges less both before and behind the eye. making 

 the free cheek more triangular and less quadrangular in outline. 



The pygidium has a wider border than C. prolifica. 



Formation and locality. — Upper Cambrian. Nolichucky shale (Loc. 

 io7a) : Bull Run Ridge, ii miles (17.6 km.) northwest of Knoxvilie, 

 Tennessee. 



Genus CHANCIA Walcott 



Chancia Walcott, 1924, Smithsonian Misc. Coll., Vol. 75, No. 2, p. 55 



Description.- — Chancia is characterized by a wide cephalon and 

 thorax. Fixed cheeks at the narrowest point nearly as wide as the 

 glabella on the same line. Palpebral lobes moderately small and 

 connected with the dorsal furrow near its front by an ocular ridge. 

 Frontal limb wide, and marked by a strong transverse furrow that 

 divides the wide rim from the border. Glabella tapering, marked by 

 a rounded median ridge and apparently faint glabellar furrows, whose 

 position and direction are similar to those of Ptychoparia. 



Free cheeks undetermined. 



Thorax with numerous segments, 20 in the genotype and 24 in 

 C. cvax. The pleural furrows are similar to those of Elrathia. 



Pygidium small, trilobed and faintly segmented. 



Observations. — Chancia resembles Elrathia, but differs in its wider 

 fixed cheeks and wider rim, but most strongly in the small pygidium. 



From Amecephalus it differs in the presence of a wide frontal rim, 

 wider fixed cheeks and occipital furrow. The pygidium, while small 

 and unsegmented as in Amecephalus, is wider and the trilobation is 

 less pronounced, due to a lower axis. The thoracic segments of 

 Chancia are blunt compared to the slender spines of the posterior 

 portion of the thorax in Amecephalus. 



Genotype. — Chancia ebdome Walcott. 



Range. — Middle Cambrian : Rocky Mountains of Idaho. 



CHANCIA EBDOME Walcott 



Plate 17, fig-. 26 



Chancia ebdome Walcott, 1924, Smithsonian Misc. Coll., Vol. 75, No. 2, p. 55, 

 pi. 10, fig. 4- V 



The illustration of this species presents its characters quite clearly. 



Formation and locality. — Middle Cambrian: (55c) Spence shale: 

 Danish Flat, six miles (9.7 km.) southwest of Liberty, Bear Lake 

 County, Idaho. 



