TRILOBITES. 707 
Isotelus canalis.] 
IsoreLus cANALIs Whitfield, sp. 
Asaphus canalis WHITFIELD, 1886. Bull. Am. Mus. Nat. Hist., vol. i, p. 336, pl. 34, figs. 1—8. 
Asaphus canalis WHITFIELD, 1889. Bull. Am. Mus. Nat. Hist., vol. ii, p. 64, pls. 11, 12. 
This name, which has been ascribed to Conrad by both Profs. Hall* and Whit- 
field,; and also by Mr. Billings,{ had no particular meaning until Whitfield described 
under it a nearly entire individual from the Fort Cassin beds on lake Champlain. 
To credit the species to Conrad is merely a matter of courtesy, as it was used only 
_ in his manuscript and even then applied to a specifically unidentifiable part of 
the pygidial doublure. The relations of that fossil, or of those described by Hall under 
this name from the Chazy limestone, to Mr. Whitfield’s species are quite uncertain. 
There are two extended and nearly entire specimens from the lower or Birdseye 
horizon of the Trenton group in Fillmore county, Minn., and a single pygidium 
Fig. 9.—Isotelus canalis? Lower Trenton, Fillmore county. 
from an equivalent position at Stanton, Minn., which may be provisionally referred 
to this species; though it is to be confessed that their differences from I. maximus 
* Palzontology of N. Y., vol. i, p. 25, pl. 4bis, figs. 17--19. 1847. 
+ Loe. cit. 
+ Paleozoic Fossils, vol. i, p. 255, p. 352. fig. 340, 1865; and Geology of Vermont, vol. i, p. 299, pl, 12, fig. 5, 1862. 
