A.MMOXnlDKA 





common in Psilocercu. A'V .->///</ <-r-.y</ /// ///. ///<////-/ acctlerat* 

 ceras, where it is hollow. 



There are two types of young in .1 ri>'i !<l<i, which al'in-wanls h.-i-min- s.-parat-.| in "ih.-r 

 related groups : a lu-uad depressed or coronate 

 type occurs in typical Arietidae and some 

 others, and the compressed /^>'/<>,;-,->i,i \\\- in 

 Arnioceras, etc. Pscud<itrojiili'l,i, >h,.u that 

 Coeloceras may have originated from Arietidae 

 through persistent development of a trapc- 

 zoidal form of young with correlative changes. 



Family 4. Arietidae. Volutin- "I 

 discoidal forms more quadrate than in pre- 

 ceding families, and often with channeled 

 venter. Costae more strongly developed as 

 a rule, and with prominent ventro-lateial 

 angles, which are sometimes tuberculated. 

 Sutural inflections reduced in number and 

 complexity as compared with preceding 

 families, and phylliform marginals re- 

 placed by saddles of more irregular aspect. 

 Ventral lobe long and narrow, with corre- 

 sponding siphonal saddle. Usually only 

 two pairs of large lateral saddles, the second often the most prominent. First pair of 



lateral lobes large, second and third 

 pairs successively smaller ; third and 

 fourth pairs of saddles also smaller, 

 the last often partially on line of 

 involution. Antisiphonal bifid, very 

 long, and sometimes complex. One 

 pair of large dorsal saddles, and one 

 of short, often incomplete lobes. 

 Anaptychus observed in several 

 species. 



Fio. 1190. 

 i/i, Drug, s] 





Fio. 1197. 

 Suture-line of Coroniferas Hsulcatum, Brug. sp. (cf. Fig. 1097). 



Coroniceras (Arietes, Waa^-n , 

 (Figs. 1196, 1197), Vermiceras, Arnioceras, Asteroceras, Tmaegoceras, Caloceras, Hyatt 

 (Ophioceras, Hyatt ; Alsqtites, Haug) ; 

 Echioceras, Bayle. Lower Lias. 



Family 5. Oxynotidae. Shells 

 compressed and more involute than in 

 Arietidae, with narrower and more acute 

 keeled venter, but no ventral channels. 

 Sutures Arietean in Agassiceras, but ha\c 

 extended and highly modified auxiliary 

 inflections in Oxynoticeras. Keel hollow 

 in adult of some species of the laltn 

 genus, and in a transitional conditi< n in 

 Aetomoceras. 



Oxynoticeras (Fig. 1198), Ayassiceras, 

 Hyatt ; Cymbites, Neum. ; (?) Faroniceras, 

 Bon. ; Aetomoceras, gen. nov. Type A. 

 (Amm.) scipionianum, d'Orb. sp. Lower 



Lias. 



i'" i'" s 



n., ,/,,( i,-i r* 



sp. Lower I. in* (3); 



Family 6. Hildoceratidae. Dis- 

 coidal involute shells have sigmoidal costae separated throughout or confluent on the 



