﻿48 BRITISH FOSSIL CEPHALOPODA. 



DESCRIPTION OF THE GENERA OF NAUTILOIDEA. 



Suborder NAUTILOIDEA. 



Group I. Conici. 

 Genus Orthoceras, Breyn. 



1732. Orthoceras, Breynius, ' Diss. Phys. de Polythalamiis.' 



1823. Ormoceras, Huronia, Stokes, ' Trans. Geol. Soc' [ = subgenus Actinoceras]. 



1824. Actinoceras, Bronn, ' Leth. Geogn.' [ = subgenus]. 

 1829-37. Melia, &c, Fischer, ' Oryct. Gouv. Moscou.' 

 1834. Conoceras, Bronn, ' Leth. Geogn.' [ = subgenus]. 

 1838. Conotubularia, Troost, ' Mem. Soc. Geol. France.' 

 1841. Bactrites, Sandberger, ' Verst. Nassau.' 



1843. Koleoceras, Portlock, ' Geol. Eep.' 



1844. Cycloceras, Loxoceras, M'Coy, ' Carb. Foss. Ireland.' 

 1847. Endoceras, Gonioceras, Hall [ = subgenera]. 



1850. Stenoceras, D'Orbigny, ' Cours de Pal. stratigraphique.' 

 1858. Tretoceras, Salter, ' Quart. Journ. Geol. Soc' [ = subgenus]. 

 1860. Cochlioceras, Trematoceras, &c, Eicbwald, ' Leth. Eossica.' 

 1867-74. Bathmoceras, Barrande, ' Syst. Sil. Boheme ' [ = subgenus Conoceras]. 



History. — The genus Orthoceras was first instituted by Breyn in the year 1732, 

 for the well-known straight Nautiloids, and no additions were made till 1823, when 

 Dr. Bigsby described, in the Transactions of the Geological Society of London, 

 some remarkable siphuncles from Lake Huron, to one of which Bronn gave the 

 name Actinoceras, and to the others Stokes applied those of Huronia and Ormoceras. 



These three will be described further on as Actinoceras. He also figured an 

 Orthoceras with remarkable chevrons over the siphuncle, which Bronn afterwards 

 called Conoceras. In 1829 and 1837 Fischer de Waldheim named some fragmentary 

 specimens Sannionites, Epitonites, Callirhoe, and Melia, the latter representing an 

 Orthoceras with a complicated siphuncle, being afterwards called Thoracoceras. In 

 1838 Troost proposed to separate the examples with a large bulbous siphuncle as 

 Conotubularia. In 1841 Sandberger established a genus Bactrites for species with 

 so lateral a siphuncle that it seemed to form a lobe in the septa ; the same was after- 

 wards called Stenoceras by D'Orbigny. In 1843 Portlock described as forming a new 

 genus, characterised by the possession of a sheath, some Orthocerata grown over with 

 some Hydractinixx or other organism, applying the name Koleoceras. M'Coy attempted 

 a subdivision of the genus in 1844, by calling the species with transverse ribs Cyclo- 

 ceras, and those with oblique septa Loxoceras. The same year saw the establishment 

 of the subgenus Endoceras by Hall, on specimens with large lateral siphuncles, 



