NO. 3 CAMBRIAN TRILOBITES 165 



MILLARDIA AVITAS, new species 



Plate 28, figs. 5, Sa-c 



This species is represented by two very distinct cranidia. These 

 differ in so many respects from the other species of the genus that 

 detailed description and comparisons do not appear to be necessary. 

 The most nearly related form is M. optata (see pi. 28, figs. 4, 4a-b) 

 from the Upper Cambrian of Wisconsin. With a strong lens the 

 surface is seen to be roughened by minute granules of varying size. 



This species is of special interest, as it serves as a link between 

 the Upper Cambrian fauna of the Appalachian trough in Pennsyl- 

 vania and that of the Eau Claire subfauna of the Upper Cambrian 

 of the upper Mississippian province. 



Formation and locality. — Upper Cambrian: (107k) Buffalo Run ^ 

 limestone, 2 miles (3.2 km.) north of Benore Post Office, Center 

 County, Pennsylvania. 



MILLARDIA OPTATA (Hall) 



Plate 28, figs. 4, 4a-f 



Conocephalites optatus Hall, 1863, Sixteenth Ann, Rept., New York State 

 Cab. Nat. Hist., p. 222, pi. 5 A, fig. 7. (Describes and illustrates species.) 



The type specimen of this species consists of the central portion of 

 a cranidium showing the glabella, occipital ring, frontal limb and 

 margin, and a narrow fragment of the fixed cheeks. 



Entire specimens of the cephalon show it to have been semicircular 

 in outline, strongly convex, and with rounded genal angles. The 

 glabella and other parts are essentially similar to those of the 

 cranidium of M. semele. The differences between the two species 

 are : the more transversely elongate outline of the cranidium of 

 M. semele; the nearer approach of the posterior end of the facial 

 suture to the genal angle in M. optata. 



Casts of the outer surface of the test of M. optata indicate that it 

 had a granular surface. 



Formation and locality. — Upper Cambrian: (79c) Eau Claire 

 formation ; sandstones at Willow River Falls, a few miles from 

 Hudson, St. Croix County; and (looa) Ettrick, Trempealeau 

 County, both in Wisconsin. Also from (84) Eau Claire formation; 

 Dresbach, opposite the mouth of Black River, Winona County, 

 Minnesota. 



The specimen described by James Hall is stated to have come from 

 the " lower beds near Trempealeau," Wisconsin. 



A provisional name suggested by Mr. E. F. Moore. 



