aT 
= 
— 
4 THE PALHONTOLOGY OF MINNHSOTA. 
(Nileus vigilans. 
rrooves Which are linear, These sulci disappear at reaching the broad margin, but 
8 B ’ 
the interannular grooves are continued upon, and nearly across the marginal 
£ pon, 
expansion, The surface appears to have been quite smooth, 
The larger of the specimens measures 2 mm. both in length and width, 
The distinctive features of this subgenus and species are those of earl 
g I 
representatives of the asaphid type, which at maturity show a condition of distinct 
annulation, The form appeared at a period when the true asaphs were on the 
PI i 
decline and near extinction. Both structure and size indicate that this was a 
paracmic modification of the asaphid stock, reproducing in the senility of the race 
the characters of immaturity. 
Formation and locality,—Utica shale, mouth of Licking river, Ohio; probably also in the Hudson 
River shales, Rome, N, Y. 
Genus NILEUS, Dalman, 1826. 
Nineus viainAns Meek and Worthen, (sp.) 1875, 
Asaphus vigilans Munk and Worrien, 1875. Geol. Sury. Tllinois, vol. vi, p. 497, pl. 23, fig. 6. 
Tllenus (Nileus) minnesotensis, Pours, 1887, Fifteenth Rept, Geol, and Nat, Hist, Surv, Minn., 
p. 478, fly. 1. 
The description given by Mr, A. F. Foerste was based upon a single cranidium 
from the Trenton horizon at Minneapolis. ‘There are before me a number of 
essentially entire individuals, most of them enrolled but several in an extended 
condition, Some of these are from Minneapolis but the majority from the Galena 
beds. Upon comparison of these with the description and original specimens of 
Asaphus vigilans Meek and Worthen, I find no basis of specific distinction, 
Wig, W.—Nileus vigilans Meok and Worthen, ig. 18.—Profile of the same specimen. 
Cephalic view of an enrolled individual, 
General form elliptical with subcrescentic extremities; longitudinal lobation 
very obscure, Cephalon transverse, regularly convex. Margin very slightly 
thickened by a thread-like elevation. Genal angles obtuse. Frontal slope full but 
not projecting, terminating abruptly .on the “margin: lateral surface slightly 
depressed beneath the eyes; upper surface between the eyes flattened. Glabella, 
dorsal furrows, occipital furrow and ring not defined. Eyes small for this genus, 
but prominent; situated at points each one-third of the entire transverse diameter 
from the lateral margin and one-third of the longitudinal diameter from the posterior 
eh @ 
