\( \NTII.M | | 



in :ibciT:mt form. /A-/-/. /////'///.-. remain- 10 be mentioned, 



, ( ,in ;||| nllier ///'///<v in the |,-ss number of 

 which it possesses, whilst ill other respect* it is c|o-.cl\ 



willicd to t in- t nu- l)fiifnin ; in rega rd to its true relations, farther 



i r\ . 



ipeoies. 



lloiM.111- MICIII Ai'iAM s. d'Orb. T. I I 'J, ligs. lil'.S. (iC'.l. 

 <irnus ACANTHOCERAS, N-uin:i\r. 



r'rom //<>!>/ //<.<. nr:ir its origin, :i l:ir_u;r sri'ics di vi-r^rs. which 

 cinl>r:icf> tin- groups: A no-iilico>t:it i. ( 'r:i>sccost ;it i. 

 i. .M:Miiill:iri's, :in<l Hot oin.-i^fii-cs. ;ind whidi. at'lt-r 



i. I si-p:ir:iti':is :m Independent genus. IsiMtrd 

 t'nnns :irc t'oiiinl. which combine the cliMi'Mcters of Acanthoceras 

 MIK! //niilifi'ti without MpitroMcliinii' the point of divergence (origin) 

 of cither. 



The (liMirno^K of the m-niis A<-<inlh<>rcras may be presented in 

 t lie following niMiiner : 



Suece^or- of tlie u'1'onp of Hopltt8 abscissus, with a moder- 

 ately wide umbilicus :md not very elevated whorls. Margin of 

 aperture Mild length of body-chamber unknown. The sculpture 

 (.n-i>t> of unite st might ribs, which become constant ly stronger 

 from the Mitnre outwards to the external side, which arc fre- 

 quently oniMmented with a greater or h-ss number of tubercles 

 or nodes, and are most curved in young individuals. The de- 

 velopment of the external side is very variable, the middle line 

 ^ometimcN with uninterrupted ribs, sometimes with a furrow, 

 Bometimefl with a line of tubercles, the elements of which attempt 

 to unite into a keel. Lobular line much reduced : besides tin- 

 two lalerals on the thinks there is at most one auxiliary, or 

 a n>w of two to three extremely -mall deep-lying auxiliaries; 

 bodies of the lobes and saddles plump and broad, the la-t 

 broader than the tir-t. no branching, but only a dentation of the 

 lobe-.. Siphonal and first lateral usually not very ditterent in 

 size, the first often larger than the la>t ; M-cond lateral much 

 smaller than the tir-t. both one-pointed. 



Thirty-six gpeci 

 A AM HOCI ..K.\> KOTOMAOBIfSI, I'.roiig. T. HI:;, tig. I 



