82 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



CORBINIA VALIDA, new species 

 Plate 16, fig. 18 



Of this species only the cranidium illustrated is known. It differs 

 in details of the outline of the glabella, occipital ring and frontal limb 

 and border, from C. horatio. 



Formation and locality. — Same as that of C. horatio. 



Genus CRUSOIA Walcott 



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



Description. — This genus is characterized by the peculiar upturned 

 front of the head, the small glabella and the extremely small pygidium. 



The cranidium is wide at the base and narrowed in front. The 

 frontal border is turned up quite sharply in the middle. Eyes are 

 extremely small, situated at the end of an eye-line at a point opposite 

 the anterior end of the glabella. Glabella about two-thirds as long 

 as the entire cranidium and rounded conical in shape. A pair of 

 posterior glabellar furrows, triangular in outline, is faintly visible on 

 some specimens. 



Free cheeks small, without genal spines. They have a definite rim 

 and a doublure of uniform width. 



Thorax with about i6 segments. The axis is convex and relatively 

 wide ; pleural segments with a narrow, nearly straight furrow within 

 a high posterior marginal rim and a narrow depressed anterior border. 



The character of the pygidium is uncertain. There are several 

 entire individuals in the collections, but the pygidium is not clearly 

 defined on any of them. It is certainly very small. 



Genotype. — Crusoia cehes Walcott. 



Range. — Middle Cambrian : Wolsey shale, Montana. 



CRUSOIA CEBES Walcott 



Plate 15, figs. 5-7 



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

 pi. 10, fig. 7. 



This species is fairly abundant at the type locality. 



The generic description together with the illustrations clearly de- 

 fines the characters of the species. 



Formation and locality. — Middle Cambrian: (4g) Wolsey shale. 

 Five miles (8 km.) northeast of Logan, Montana. 



