i i; \. HTI IB \-. OB 



by their broad Diddle B talks, \\ith dm-ioiis .-ut in 

 obliquely. tin- oblique position of tin- tip- ul' the In!- 

 velopiueiil of the principal lobes. Miid >trikini: ivdm-timi <>f 

 auxiliary ODGS. 



Kle\eii Tria-sie species. 

 TKO|'ITK> I J A M> \ i KI: i, ( Jiu-nsl . T. lll,li_ 57. 



TRACHYCERAS, 



l'x(ly-cli:nnl)rr short, one-hall' to l\v<>-tliinU of :i whorl Ion-. 

 The sculpture on the convex portion i> inti-rruptrd : in the geo- 

 loui<-:illy younu'er I'onns n more or less deep medinn furrow i- 

 BUnken in, at which the ribs U'nninate in ;i t ulierele. Apejiui-e 

 with:i short lol>:iU- jiroeess on tlie convex portion. Lole> agree- 

 ing with Trojiid'x: niuch simpler in l he geologically older forms. 



Sixteen Trins^ic species. 



TBACHYCERAS HICRENATUS, Htiuer. T. 101), figs. r,41. 



Genus CHORISTOCERAS, Huuor. 



From Trurhyceras a group branches off, distinguished by a 

 lamer growth and simple or slightly toothed lobes, with a short 

 l>ody-diaml>er. in which, on the inner whorls the median inter- 

 ruption of the sculpture on the convex portion is almo>t alway- 

 visihle. whilst on the outer whorls the ribs are continuous over 

 the eon\ex portion. It is also to be observed that on one hand 

 tin- lobes exhibit the persistence of an ancient xtagi of develop- 

 ment. and on the other ;i special variation from the sculpture of 

 the Trarht/rtTfis type. 



Nine Triassie species. 



Genus RHABDOCERAS, Ham-r. 



Rod-like, elongated forms with oblique annular sculpture and 



simple curved lobes ; still very imperfectly known, and an . 

 cording t< :ill probability, to be placed next to ('/t<>ri*fu<; 



RBABDOCKLAS Si BSSII, llauer. T. 100. ligs. 513, 514. 



Genus COCHLOCERAS, Hauer. 



The whorl- are -pirally coiled to the left, with continuous 

 rit and -imple curved lobes. This form also may be placed 

 ' ' ; M//vW'"-r/v/s. 



Fix-iiKKi. Ilaner. r \\ 1 oil. lig^. ." I s. ;,19. 



