1732. Orthoceras, Breynius 



A. 1844. s. g. Endoceras, Hall 



CEPHALOPODA . 227 

 Genus Orthoceras, Breynius. 



1. 1834. Actinoceras, Bronn. 



2. 1837. Ormoceras, Stokes. 



3. 1837. Conilites, Pusch. 



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, McCow 



11. 1851. Trematoceras, . Eichwald. 



12. 1857. Cochlioceras, Eichwald. 



13. 1857. Dictyoceras, Eichwald. 

 k 14. 1860. Heloceras, Eichwald. 



1. 1842. Cameroceras, Conrad. 



2. 1850. Colpoceras, Hall. 



3. 1860. Nothoceras, Eichwald. 



B. 1823. s. g. Huronia, Stokes. 



C, 1847. s. g. Gonioceras, Hall. 



The species of the genus Orthoceras 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 



