ORDER li 



AMMnNolDKA 



//,, futures iiifi finillit, anil tn nmll/'j,/,/ ,i ,!, ,,f /,,/> ,i,nt 

 i.i-ti-rniillii it/nl mi tl/, <lt>r*n in. /'//.<;/ lnt,/;il ./(/<//..> n/it t<> 

 three di*tini-t 



Family -J.-1. 



in prOpOfftOB) /'"'/' 

 in l<it> / 



Sphenodiscidae. Suture- -lightly more romp]e\ than tho.-e 

 and \\ith phylliforiii marginal-; dor.-al- nionophyllir. 

 to those of Engonoceratidcki 



in ]>rimitive species, and have con- 

 cave venter.- and rompiv--ed volu- 

 tions. Venter subaeute or keeled 



ill the adult, but later lo-e- ii- keel, 

 and becomes plano-convex or 

 rounded. 



Sphenodiscua, Meek; /"//</<< r*. 

 Xoetling ; Libycocera^ gen. nov. 

 (Fig. 1224). Type L. (Spkm. 

 Ismaeii, Zittel. Cretaceous. 



Family 23. Placenticera- 

 tidae. Tuberculated and smooth 

 forms, the young of which pa-- 

 through a stage \vith smooth, Hat, 

 or concave venters similar to adult 

 of Engonoceras. Venter remains 

 flat or compressed until old age, 

 when it becomes rounded. Sutures 



remarkable for their complex, D ^^[^ SXS.' 

 irregular, ragged outlines, and 



narrowness of saddles. Their outlines in the young very similar to those of fy//./' 

 discidae. 



riticenticeras, Meek ; Diplacomoceras, gen. nov. Type I). (Amni.) 1>i<lrfnin*. 

 Schliit. sp. Cretaceous. 



Family 24. Engonoceratidae. Compressed shells witli numeroii.- sadd: 

 e'incave or flat venter. Costae nodose in Mum- .-jiecit-s, but usually fold-like and 

 sometimes merely broad, low lateral >wellings. Sutures >impler than in >'/-//'/'"- 

 discidae, but of the same type. 



Engonoceras, Neum. ; Knemiceras, Bo'lim ; Xeolobites, Fisi-lu-r : /'/,/. 

 gen. nov. Tyj.e /'. (A nun.) (,'<ihl,,\ Hyatt = Amm. j t ,-<l>Tii<ili}i, Clabb. 



' Ii;- 1 " 4- 

 Libycoceras Ismaeli, Zittel sp. Upper SeiKiiiian ; 



Libya 



IX. ACANTHOCKKATIOA. 



A series of more or less uncoiled genera connect"/ tJinmiil, tl,, trnn*itii>i<iil A>-'Hitli<)- 

 ceratidae with normal Cretaceous *//"//* Jmring costae inti>rni}if><l m> flu' ri'nl<r f mmh- 

 stage or throughout life, although in most forms cmtimniii* during later stage* f tl<. 

 ontogeny. 



Family 25. Acanthoceratidae. Young slender, discoidal, without inl- 

 and section rounded until late in neanic stage. Sutures have diM-ply-.-ut outlines, 

 and owing to frequent presence of only >i.\ lolu-s and saddles simulate those of 

 Leptocampyli, but are not of tin- same type. First lateral >addle> l>nad and 

 bifid; ventral lobe straight, deep, and has a trmic-utrd .-iph<>nal saddle. lv\t-rnal 

 characters similar to some forms of Jf<i/>lifiil<tfi. Some species have costae bifur- 

 cated, more or less interrupted, and with only the ventm-lateral row of tuherde.- 

 or none. 



Acanthoceras, Neum. ; 77n/ ////<'/////-/, gen. nov. Type '/'. (Amm.) TIinn,ni,i,,i, Pi-t. 



