ll Til ISM \. t.oN|o< T.RAS. K/l'r. 



Tretoceras, Suiter. 

 l-'oimded on 0. Iti^ifihoiKitu in. So\vl.. tVoin the CaradMc sand- 



stoiu- ( Silurian ). IJrit.. in \vliicli the septa are apparently perfo- 

 rated ly t \VM siphnncles ; one of \vliicli is M deep lateral cavity 

 continuous with the terminal chamber tin- cavity affecting MI 

 least seven oi' the iippennost septa. it' not the whole. 

 T. Hisii'iiMN ATI;M. Sowl>. IM. !>7. ii"-. 4Sl. Siliirinn. 



Thisoa, Monti. 



Shell ovate-elongate, cucumber-shaped ; :ipp:nvntly two siphon^ 



fiinnini:- |):irnllel the whole length of t he shell, one of which tr:iv- 

 erS68 a soi-t of nurrow Intend r:i\it\ ; there :ire ;dso M nnndier 

 of false siphons or holes, which do not extend tin 1 entire length 

 of the shell. 

 T. SIPHON :\i. is. Serves. 1*1. 1(14. fi<rs. .".T 1 . ^~\'l. .lur.Mssic. 



Gonioceras, Hall. 



Shell ll:ittene(l. with extrenielv s.-dient nnu'les : septa siniuni-. : 

 section of shell. Mil extended ellii)se with projecting Mliii'les ; 

 siphniicle vent i';il. 

 (i. \\CKI-S. H.-dl. IM. 97. fii-s. 4x:i. 4,s4. L. Silnrinn. 



Colpoceras, Hall. 

 Tliis is prnl:iMv only a siplion of one of the laru'er spt-cics of 



Orthocerata. 



('. VTEQATUM, Hall. IM. ( .>7. tin'. 4s5. L. Silurian, \i-tr }'</,-. 



Dictyoceras, Eichw. 

 Is prolialdy an ( )rt hoceras covei-ed ly :i l>ryoxoan or coral. 



Genus CLINOCERAS, Masck.-. 



Shell conical (allied to LoxOCeriS, McCoy), the siphnncle side 

 -i raiiiht. t he others more or less cni'Ncd; a constriction In-low 

 the ltody-ch:imocr. Seittal border with an olt nse-aiiu'h'<l saddle 

 on the >iphnncle side, with uvntly rounded lohes and two slight 1\ 

 marked lateral >addles. 



('. I.KNS. Ma>ckc. IM. I (if., ftg. 687. Krratic L. Silurian blocks. 

 Prussia. 



