ORTHOCEEATID^. 
57 
1866. Ortkoceras nochcostatum,WCh.esiiej, Trans. Chicago Acad. Nat. 
Sci. vol. i. p. 53, pi. ix. f. 5 ( fide J. Hall). 
1867. Ortkoceras annulatum, Hall, 20th Keg. Rep. p. 351, pi. xx. 
ff. 4-6. 
1868. Ortkoceras annulatum ?, Worthen, Geol. Surv. of Illinois, yol. iii. 
p. 117. 
1870. Ortkoceras anmdatum, Hall, 20th Reg. Rep., revised edition, 
p. 411, pi. xxiv. flf. 2-4. 
1875. Ortkoceras annulatum, Hall & Whitfield, in Newberry’s GeoL 
Surv. of Ohio, vol. ii. pt. ii. p. 147, pi. ix. f. 1. 
1882. Ortkoceras annulatum, ^\'hitfield, in Chamberlin’s Geol. Surv. of 
Wisconsin, vol. iv. pt. iii. p. 298, pi. xix. f. 1. 
1884. Ortkoceras annulatum, Whiteaves, Palreozoic Fossils, vol. iii. 
pt. i. p. 38. 
I think that there exist sufiiciently well-marked characters in the 
American form of 0. annulatum to make it desirable to separate it 
from the European one, and, accordingly, 1 propose the above de- 
signation for it. 
The characters by which the variety Arnerlcanum is distinguished 
from its European allies reside in the surface ornaments. These 
consist of transverse elevations, partaking more of the nature of 
undulations than of ribs, and becoming in some places indistinct, or 
even obliterated. The undulations are generally wider than the 
spaces separating them, being at a distance of about -J- the diameter. 
The fimbriic are coarse, as in the variety crassum, but with their 
arches or festoons much wider apart. Three or four only occupy 
the spaces between the undulations. The longitudinal elevations 
are sometimes so strong as to cause a nodose appearance ; but this 
is not always the case, as I have a specimen before me in which 
they are very obscure. The rate of tapering in a somewhat flat- 
tened example from Canada, measured along its broader diameter, is 
1 in 17. 
Horizon. Niagara Group (Wenlock). 
Localities. Canada; Lockport, New York State; Ripley County, 
Indiana. The specimen from Canada was presented by the late 
Dr. J. J. Bigsby, E.R.S. 
Yar. fimbriatum, Salter. 
1839. Ortkoceras Jimbriatum, Sowerby, in Murchison’s Sd. Syst. p. 632, 
pi. xiii. f. 20. 
1854. Ortkoceras anmdatum, var. jimbriatum, Salter, in Murchison’s 
‘ Siluria,’ p. 232, pi. xxvi. f. 2. 
1868. Ortkoceras annulatum, Barrande, Syst, Sil. de la Boheme, vol. ii. 
Texte iii. p. 308, pi. ccxci. If. 7, 8, 10-14, pi. ccccxli. f. 1. 
