CEPHALOPODA. 
907 
U LJ I 
Genus Ortiioceras, Breynius. 
1732. Orthoceras, Breynius 
A. 1844. s. g. Endoceras, Hall . 
B. 1823. s. g. Huronia, Stokes. 
C: 1847. s. g. Gonioceras, Hall. 
1. 1834. Actinoceras, 
Bronn. 
2. 1837. Ormoceras, 
Stokes. 
3. 1837. Conilites, 
Puscii. 
4. 1838. Conotubularia, 
Troost. 
5. 1843. Koleoceras, 
PORTLOCK. 
6. 1829. Melia, 
Fischer 
7. 1837. Sannionites, 
> DE 
8. 1844. Thoracoceras, 
Waldheim. 
9. 1844. Cycloceras, 
McCoy. 
10. 1844. Loxoceras, 
McCoy. 
11. 1851. Trematoceras, 
Eichwald. 
12. 1857. Cochlioceras, 
Eiciiwald. 
13. 1857. Dictyoceras, 
Eichwald. 
14. 1860. Ileloceras, 
Eichwald. 
f 1. 1842. Cameroceras, 
Conrad. 
1 
2. 1850. Colpoceras, 
Hall. 
^ 3. 1860. Nothoceras, 
Eichwald. 
The species of the genus Ortiioceras described in the following pages 
embrace those at present known from the Schoharie grit and Upper Helder- 
berg limestone, the Hamilton. Portage, and Chemung groups. The Schoharie 
grit is separately mentioned in this place because the Orthoceratites are more 
numerous, both in species and individuals, in that rock than in any other mem¬ 
ber of the series, except perhaps in the Hamilton group. In the one case, we 
have a formation of about thirty feet, and the other has a thickness of one thou¬ 
sand or twelve hundred feet in its greatest expansion, gradually thinning to 
three hundred feet in its western extension. The difference in the amount of 
accumulated material in the two formations is extremely great; and we may 
infer that the difference in time was in some degree correspondent. 
The Schoharie grit consists of a coarse, irregular rock, varying from a 
r 
