NO. 3 CAMBRIAN TRILOBITES 185 



make the species an intermediate form between Conocephalites, Alo- 

 kistocare, and Menomonia, as far as comparison may be made with 

 the cranidia. The frontal Umb with its median boss and strong, 

 rounded frontal rim suggests Acrocephalites; the broad fixed cheeks 

 and slightly pitted outer surface, Alokistocare, and the strongly 

 defined subtriangular glabella and occipital ring, Menomonia. Noth- 

 ing more is known to me of the species than is shown by the illustra- 

 tions. The test usually adheres to the matrix so as to show its 

 interior surface ; small fragments indicate that its outer surface is 

 pitted or punctate, which may account for its adhesion to the matrix. 

 The largest cranidium has a length of 12 mm. 



Formation and locality. — Middle Cambrian: (5!) limestone inter- 

 bedded in the Wolsey shale, Meagher County, on the road to Wolsey, 

 about 4 miles (6.4 km.) south of the divide at the head of Sawmill 

 Creek, and 11 miles (17.7 km.) south of Neihart, Little Belt Moun- 

 tains, Cascade County, Montana. 



ALOKISTOCARE LINNARSSONI (Walcott) 



Plate 25, figs. 7, ya 



Ptychoparia ? linnarssoni Walcott, 1884, Monogr. U. S. Geol. Survey, Vol. 8, 

 p. 47, pi. 9, figs. 18, i8a. (Description and illustrations of typical cra- 

 nidia of the species.) 



This is a fine species known only by its cranidium and free cheeks, 

 which are well shown by the illustrations. The outer surface of the 

 test has been more or less injured by weathering, but it indicates 

 that, it was originally minutely pitted or punctate. The character of 

 the frontal margin of the cranidium is indicated by the fiat rim of 

 the associated free cheek, except that the rim thickens and is 

 separated by a scarcely perceptible depression from the frontal limb. 

 The largest cranidium in the collection has a length of 11 mm. 



The most nearly related species, A. ? prospectense, occurs 3,000 

 feet lower down in the Eureka district section. They both have a 

 rounded frontal limb and rim, but that of ^. f prospectense is shorter, 

 and the palpebral lobes are larger and further back on the fixed 

 cheeks. 



Formation and locality'. — ^Middle Cambrian: (58) shaly lime- 

 stones in upper beds of the Secret Canyon shale ; east side of New 

 York and Secret Canyons, Eureka District, Eureka County, Nevada. 



Upper Cambrian: (15J) Orr formation; southwest part Fish 

 Spring Range; and (i5t) near south end Fish Creek Range, both 

 in Toole County, Utah. 



