20K oKTHorKKAS. CA.MKKorKK \s. KT<'. 



droid, small. marginal, tin- si|)h}ii:il investment more or less 

 solid :uul persistent. 



|-'"->il only. about hidii specie- (M known. 



F:iinily I. NAl'TIUIU-;. 

 (ii-nus ORTHOCERAS, IJn-vn. 



Shell straight : aperture somet hues contracted. 



Fossil. *24o species. L. Silurian to Liassic ; X. America. A HS- 

 1 r:ili:i. Kurope. 



Probably the :iniin:il was nol aMe to \vitlnlr:\v itself completely 

 into its shell, us in the \Miitilns. That the shell was external is 

 indicated \\\ the colored liands preserved on <>. u //</tt/ i/rriix. 



These shells attained sometimes "Teat si/e : a specimen in t he 

 collection of Mr. Trite, of Alnwick. Knirland. must have lieen 

 -ix feet lonr when perfect. <). '/'ini/i is esiimatdl to have 

 weighed ' >ome ton-."' The aperture is >ometimes so con- 

 tracted that speeie> two feet in len'tli luiven diameter of only 

 one inch at the mouth. 



O. I-I.AMCA.X AI.ICI I. ATI M. Saudi). |M. '.Mi. ii^. 470. I >e voiii:i ii. 



Nassau. 



a. si I;\\M i,.\iu:. llarr. 1*1. '<;. ML:-. 471. Silurian. Hnhi'mia. 

 The followinu' sid>iiTiiera or o-rnups are i-ener:illy adopte<l : 

 Cameroceras, ('<nr;nl. 



Siplmnele lateral, sometimes very lar^e ( simple ?). 

 Twenl \-se\-eii species. L. Silurian to Triassic'.' A". 



C. VKKMK i LARI8, d'Areh. PI. '.;. li-. 4 



('. \A.I\\TIS. Schloth. PI. '.HI. fi-r. 47.'5. 



Act:noceras, (Hn.wi 



Siphuiiele very lar^e. intlated between the chambers and con- 

 nected wiHi a slender central tube by radiating pl:H 



Six species. L. Silurian to Carb. N. A)m*rirn. Hurn/n . 

 A. Kirn \!5iso\i. Stoke^. PI. IM;. li^. Ht. /,. \Vmnrpe,g. 



\. p.n.suvi. pi. ( .n;. li-. 17:.. 



Newberry, Palseont. Oliio, i, 203. 



