208 ORTHOCERAS, CAMEROCERAS. ETC. 



droid. small, niar.oinal. the sii)lK)iial investment more or less 

 solid and persistent. 



Fossil only, altont KiOO species {'f) known. 



>• Family I. NAUTILID.F. 



Genus ORTHOCERAS, Buyn. 



Shell straight; apertnre sometimes contracted. 



Fossil, 240 s])ecies. L. Siluiiaii to Liassic ; X. America. Ans- 

 tralia, Europe. 



Probably the animal was not al)le to withdraw itself completely 

 into its shell, as in the Nautilus. That the shell was external is 

 indicated by the colored bands preserved on 0. anguliferus. 



These shells attained sometimes great size ; a specimen in the 

 collection of Mr. Tate, of Alnwick, England, must have been 

 six feet long when perfect. 0. Titan is estimated to have 

 weighed " some tons." * The aperture is sometimes so con- 

 tracted that species two feet in length have a diameter of only 

 one inch at the mouth. 



0. PLANICANALICULATUM. Saudl). IM. 9(i, tig. 470. I>evonian. 



Nassau. 

 O. suBANNULARE. BaiM". PI. '.»(i, fig. 471. Silurian. Bohemia. 

 The following subgenera or groups are generally adopted: 

 Cameroceras, Conrad. 



Siphuncle lateral, sometimes very large (simple?). 



Twenty-seven species. L. Silurian to Triassic ? N. America, 

 Europe. 



C. VERMicuLARis, d'Arch. PI. 96, tig. 472. 

 0. VAGTNATUs, Schloth. PL 96, fig. 473. 



Actinoceras, (Brown), Stokes. 



Sii>huncle very huge, inflated between the chambers and con- 

 nected with a slender central tnbe by radiating plates. 



Six species. L. Silurian to Carb. N. America. Europe. 

 A. RiCHARDSONi, Stokes. PI. 96, fig. 474. L. Wimiejyeg. 

 A. BiGSBYi. PL 96, fig. 475. 



Newberry, Palseont. Ohio, i, 263. 



