NO. 5 II'PEK CAMBRIAN TRILOBITES RESSER 43 



ENONTIOURA TYPICALIS, new species 



Plate 6, Figures 37, 38 



The generic description, together with the illustrations, presents the 

 characteristics of this peculiar form. 



Mendha limestone; (loc. 88) 7 miles north of Bennett Springs, 

 Highland Range, Nevada. 



Holofy pe.—U. S.N. M. No. 108696. 



MACELLOURA Resser, 1935 

 MACELLOURA TRANSVERSA, new species 



Plate 7, Figure i 



When first observed this pygidium was thought to represent M. dio. 

 Comparison shows that, while typical of the genus in every respect, 

 the pygidium is wider than that of M. dia. 



Wilberns formation; (loc. I4f) Bartlett Hollow, Burnet County, 

 Texas. 



Holotypc— U.S.N. M. No. 108698. 



ARAPAHOIA Miller, 1936 



Arapahoia Miller, Journ. Pal., vol. 10, No. i, p. 24, 1936. 



Hcsperaspis Stoyanow, Bull. Geol. Soc. Anier., vol. 47, No. 4, p. 469, 1936. 



At the time Arapalioia was originally described, only the cranidium 

 was known to the author. Specimens from the eastern front of the 

 Beartooth Mountains identified with the genotype A. typa now add 

 the Hbragene and pygidium. 



In the original description Miller pointed out the relationship of 

 Arapahoia to Plcthometopus, which occurs in younger Upper Cam- 

 brian strata. From the present study it becomes clear that Norwood- 

 ella described later is also related and that Arapahoia, Norwoodella, 

 and Plethornetopus form a single line of development. Thus far 

 Arapahoia seems to be confined to horizons in the lower part of the 

 Cedaria zone, and is the oldest genus of this group. 



In spite of the abundance of examples, it is difficult to free good 

 specimens of Arapalioia, because the matrix is refractory. 



Exfoliated cranidia have well-defined dorsal and occipital furrows, 

 and some species have three pairs of short glabellar furrows. A node 

 on the base of the occipital spine may possibly be a median eye. 



The Hbragene is of moderate size. In some specimens a border is 

 faintly indicated, but it scarcely breaks the even curvature as the 

 ocular platform slopes to the margin. The entire Hbragene extends 

 into a longer or .shorter genal spine. 



