II \MM \T>, | |; \^. n | | , ,,, BfcAt, 



smooth mi the lir-l Or Second \\lnrl. the tiil.rrdr- begin <>n 

 either the M-eoiid or t liinl \\ In >rl. :i in 1. gradually <li \ id ing. -pivad 

 them-ehe- mil II|H.II t lie abdomen as bifnreated pihe. which di-- 

 appear on tin- borders of t lie channel-. Tin- keel 111:1 ke- it ^ :i p 

 pearance at :in early stage. probably on lln- second \vli<rl. Imt 

 the channels are nol visible until a much later period. an<l li>- 

 apiu-ar ill the adult. Al>doinin;il lohe l.rond :ind deep. Sii|)erior 

 later.-d l>roader. luit of nliout the -.-line dept h ; inlrrinr l.-iteral 



\ci-\ --hallow. Superior and inferior lateral cells equally divided ; 



both are short . liroad. and luit slight l\ indente<l 1\ the minor 



lobes. 



Middle and Upper Lias. 



II AMMATOCKKAS. Alxloineii inav lie eit her rounded or acute. 

 always keeled, but never sulcated. Pihe HIT prominent and 

 straiu'ht. Envelopment may extend over one-half the sides, or 

 only cover the abdomen of each internal whorl. The j'Oimg de- 

 velop as in Phijmatoceras, but are generally much broader; the 

 pihe. also, do not become prominent so soon. Nor do they in- 

 variably beg-in by the development of tubercles on the sides, but 

 may make t heir appearance as line, raised lines, and afterwards 

 become tuheretihited. During the earlier stages of growth the 

 diilerent species have a very close resemblance to the adult 

 Macrocephali. The lobes are more complicated than in Phyma- 

 toceras. Abdominal lobe broad and deep, and continued into 

 two long, narrow, minor lobes. Superior lateral narrower than 

 the abdominal. Inferior lateral hardly wider than the minor 

 lobes of the superior lateral, and of about the same depth. Ab- 

 dominal cell blunt. Superior lateral and inferior lateral very 

 narrow and deeply indented by the minor lobes. 



Middle and Upper Lias. 

 II. INBIGNI8, Schloth. T. 108, figs. i;^4, <;_>:>. 



PKI.F.< OOEBA8. Having but one species of this genus, it would 

 be exceedingly h:ix:i rdous to give the generic characters. They 

 will, however, probably be found to be distinguished by the pe- 

 culiarly pointed aspect, shallowness ami hivadth of the lobes 

 and cells; the limits of the envelopment, which last is greater 

 than in other genera of this family: the acute form of the back, 

 :nd the breadth of the whorls. 



Upper Lieu. 



