AMMoNnll.KA 



umbilical but no true lnt'Tnf zoi\ a have '// /"'' 



throughout life. Costa<- n/>f to i continuous u,-i;,.<.< >/ yen in .>/.r/.///.> J _/',,/,,- 



?/;i& 6oM channels and AwVx. .Some genera, however, /" (<.<//.- ,lii-i,l,;l ,, //,, 



or suppressed, but there is no continuous nu'<li<in /////;//. A'-. 7 .<//,/ ,//,, /,/,.>,/. 



Family 13. Dactylioidae. Di-euidal lorm> \\ith i-o.-l:n- l.ifnn-ati-<l and alwa\- 

 croasing the venter. Sutures with v.-rv .-.implex ..mlim-, l.ut only tlir-,- or four juiir- 

 of lateral lobes and srnMlu.s Doi-sal >utnn-> ha\t- two pair- ,,f silill.-.- and on.- pair .f 

 zygous lobes. 



This series is usually termed tlu- 1'lonulnti <,[' tin- Lia>. l.ut althuu^li an dllVlmot <f tin- 

 same common stock it is (juitc distinct from its suppo^-d cuii^.-ni-i-s of tin- Middli- and I'pjicr 

 Jura. Sutuvt-s an- straight, not inclined apicad as in /'- n'x/i/i <,!</ />/,-. Tin- tainil\ ron,. 

 prises a complete cycle of forms varying fnun tin- l>nad liapi-xoidal, tabercalated \o)ution-> 

 of Coeloceras through Armatoid species to A/C////W.-/VS, in which the costae are smooth and 

 sometimes c\.-n single. 



Coeloceras, Derocera* Fi t ^. 1^).~) , />ic/////.v/v< (Fig. 120G;, Peronocerag, Hyatt ; 

 Pimelites, Diaphorites, Fucini ; (?) Praesphaerocerds, Lev! ; (?) Collii>, Uuckm. 

 ^liddle and Upper Lias. 



Family 14. Stepheoceratidae. l.uckiiian. Primitive radicals, highly coronate, 

 discoidal, giving rise apparently to involute and partially compressed forms that in 



I-'M;. I-JIM;. 



England. 



UI>IT i. 



Ki;. 1205. 



A, Deroceras subarmatuin, Y>un^ >p. 

 Whitl.y, Yorksliiiv. /;, Sutuiv-lii,,- ,,t 

 Coelocems pettos, Quenst. Mi.l.llc Lias. 



FIG. 1207. 



>'/,/<, /</(* I', i-<iii ii n ;r/;, Snvl. 

 ; Bayeux, Calvados. 



Inferior 



Macrocephalites and some others are without tubercles. Venter always rounded, 

 costae bifurcating on the sides and continuous across the venter. Only one line of 

 nodes or tubercles at the umbilical shoulders, and division of costae takes place along 

 these lines in most forms. Sutures of the same type as in M/rtyh'n/W./,, but much 

 more complex, with usually more inflections, and lobes and saddles more nearly 

 equal. Dorsal sutures generally have three pairs of zygous saddles and two pairs of 

 lobes in coronate discoidal forms. 



