20* ORTIIOCKK AS. , .\ M KK.< >(' KRA S. F/1V. 



droid. small, marginal, the siphonal investment more or less 

 solid :ui(l persistent. 



Fossil only. :il)out lr,o<> species ('( ) known. 



Family I. NAI'TILID.K. 

 (4,-nus ORTHOCERAS, Hn-vn. 



Shell straight J aperture sometimes cont meted. 



Fossil. '24(\ species. L.Silurian to L'wssio ; X. America. Ans- 

 t r;ili:i. Kurope. 



I'rohnhly the nil him I was not able to withdraw itself' completely 

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

 indicated ly the colored hands preserved on O. anguliferus. 



These shells attained sometimes o-reat size; a specimen in the 

 collection of Mr. Trite, of Alnwick. Kiio-liuul. must h:ive heen 

 six feet lono- when perfect. (). Titan is estimated to have 

 weighed ' some tons/ 1 * The aperture is sometimes so con- 

 tracted that speeies two feet in length have a dia meter of only 

 one inch at the mouth. 



<). iM.ANiCANALlou.ATr.M. Sandh. PI. !('). lio. 4T<>. Devonian. 

 Nassau. 



O. si BANM LAKK. UMIT. I'l. !('). fiir. 471. Silurian. P>oh<*nnn. 

 The following siilo-enera or groups are generally adopted : 

 Cameroceras, Conrinl. 



Siphunde latei-al. sometimes very l:ir<re (simple''). 



Twenty-seven speeies. L. Silurian 1oTriassic v A". Amerirn, 

 Europe. 

 (\ VERMICULARIS, d'Areh. IM. !Mi. li-. \~cl. 



C. VACINATI S. Schloth. JM. 9C,. fiir. \~l\. 



Actinoceras, (Brown). Stoki-s. 



Siphnncle very lai'^e. inflated hetweeu the ehaml*Ts and con- 

 nected with a slender cent ml tuhe l>y ra<liatino- plates. 

 Six species. L. Silurian to Carh. N. Amerira. 



A. IJirHAKPSoM. Stokes. PI. 90. fio-. 174. /,. 

 A. BlGSBYI. IM. '.1C. ti-. 475. 



Newberry, Palaeont. Ohio, i, 263. 



