ORDEB II 



AMMONOIDKA 



Keel may lierom.- vcr\ prominent ;iinl lillel with -|<-rial -h<-ll-layi ~, l.iit 



never hollow. Youn^- generally smooth, oompreaBed, and .-imilar to tho-.- ..r ///'/,/,,- 

 ceratidae. 

 Oecotrmitt'*, Oppelia Kig. 1100), Waagen'; Hecticocerat Lunvloeera^ 



Middle Jura. 



IV. I'liY.MATOIDA. 



Similar tn Arii'ii'in /',/ tin'/ >,!,!, _/'/</////// /'lie/in/,:^ tome diacoidal radical forms ///////</ 

 ami channels. Volution* <i<'m'i-allij atnnli-r^ I'oKtae coarser ami //>/;/'/, ami nl., mart 

 apt to become bifnn;if,,/ ,md to develop nodes. Young ^/,/-/v///// y ><.<.< /A/-',//,/// ,t nodose 

 coronate stage. Keel hollow in the adult, but solid in the young, extreme </', ami in primi- 

 tive forms. Connection n-itli Oxynoticeras improbable, since the hollow keel appears to 

 < risen independent I if. 



Family 9. Amaltheidae. Buckman, p.p. Discoidal and involute -hrll-, tin- 

 young of which have fold-like costae rising into heavy node- ju-t in-id<- tin- line- of 

 involution. Costae become prominent and sharp 

 at umbilical shoulders and veiitro- lateral angles, 

 and true tubercles appear in some Zurcherinae. 

 Venter keeled and sulcated in discoidal forms, 

 the keels alone persisting in more involute 

 species. Keel solid and crenulated by passage 

 of costae or folds across the venter. Anaptychus 

 present. 



A. AMALTHEINAE. Nodes prominent in 

 young of primitive species ; costae with only 

 one row of tubercles in later stages or none ; 

 keel invariably present and crenulated. Amal- 

 theus, Montf. (Fig. 1202) ; Paltopleuroceras, 

 Buckm. (Pleuroceras, Hyatt). Middle Lias. 



B: ZURCHERINAE. Young usually have 

 gibbous volutions with a single row of nodes, 

 which either persist, or are followed by a bi- 

 spinous stage, and inner ends of the short costae 

 also become tuberculated. Venter smooth at 

 first, and may remain so or have a solid keel. 

 Costae single, and usually bend at ventro-latnal 

 angles toward the keel, but do not cn><- th. 

 venter except in late stage of Pseudotropites. 

 Zurcheria, Haplopleuroceras, Dorsetensia, Buckm. ; Pseudotropites, Canav. ; Cana r,/ ///,.<, 

 g. nov. Type C. (Ariet.) discretum, Canav. sp. Lias to Inferior Oolite. 



Family 10. Phymatoidae. Discoidal forms with single or bifurcated costae, 

 keeled and often channeled venters. Young similar to those of Hildoccnn;,l,i,- ;n id 

 Paecilomorphidae in compressed forms. Keel hollow. 



Phymatoceras, Hammatoceras, Hyatt ; Lillia, Bayle ; Haugia, Polyplectus, Char- 

 tronia, DencJcmannia, Buckm. 



The type of Phymatoceras is Amm. Tirolensis, Dumortier, the so-called P. robust mn, 

 Hyatt, having proved to be identical with the young of that species. Upper Lias and 

 Inferior Oolite. 



Sub-Family SOXNIXIXAK. Buckman. Sonninia includes discoidal form.- with 



keeled but not channeled venter, and sides with coarse bifurcated costae diverging from 



a row of nodes along the median line of the rounded -ide<, and continued internally 



by single costae. Witchellia has nodes only in the young, and costae become single or 



VOL. I 2 P 



v.Milral Mirtaci'. This is li..iiinl<,-ous with the 

 black layer " of .\nntili'*. 



