NO. 3 CAMBRIAN AND OZARKIAN TRILOBITES 8l 



CHANCIA EVAX, new species 



Plate 17, fig. 2^ 



Observations. — C. evax differs from C. ehdome in having at least 

 24 thoracic segments instead of 20, the uncertainty as to number 

 being due to the incompleteness of the posterior portion of all speci- 

 mens in the collection. C. evax has a wider rim in proportion to the 

 border, but is essentially the same in other respects. 



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

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

 County, Idaho. 



Genus CORBINIA Walcott 



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



Description. — Corbinia is founded on the cranidium and associated 

 free cheek and pygidium. The cranidium has a strongly defined, 

 slightly subconical, truncated glabella, strong occipital ring, very 

 narrow fixed cheeks and a flattened frontal border that turns up 

 somewhat as does the frontal border of Eurekia (fig. 13, d1. 16). 

 The associated"pygidium is small, with a very strong axial lobe marked 

 by one furrow and the pleural lobes have about five short, broad spines 

 on the margin. 



A second species, C. valida Walcott (fig. 18), is represented by a 

 single cranidium. 



Corbinia differs by the form of its frontal limb and border from 

 nearly all genera except Eurekia. (For comparisons see p. 89.) 



Genotype. — Corbinia horatio Walcott. 



Range. — Ozarkian : Mons formation, Clearwater Canyon, Alberta. 



CORBINIA HORATIO Walcott 



Plate 16, figs. 19-22 



Corbinia horatio Walcott, 1924, Smithsonian Misc. Coll., Vol. 75, No. 2, 

 p. 55, pl. 10, fig. 5- 



The illustrations and brief notes under the genus give all that we 

 know of the species. 



Formation and locality. — ^Ozarkian: (65X) Mons formation. North 

 side of Clearwater Canyon, two miles (3.2 km.) from the divide at 

 head of Canyon, about 21 miles (33.8 km.) in an air line north of 

 Lake Louise Station on the Canadian Pacific Railway, Alberta, 

 Canada. 



