ORDER IL AMMONOIDEA 577 
species. Keel may become very prominent and filled with special shell-layers, but 
never hollow. Young generally smooth, compressed, and similar to those of Hildo- 
ceratidae. 
Occotraustes, Oppelia (Fig. 1100), Waagen; Hecticoceras (Lunuloceras), Bonar. 
Middle Jura. 
IV. PHYMATOIDA. 
Similar to Arietida in that each family includes some discoidal radical forms having 
keels and channels. WVolutions generally stouter, costae coarser and larger, and also more 
apt to become bifurcated and to develop nodes. Young generally pass through a nodose 
coronate stage. Keel hollow in the adult, but solid in the young, extreme age, and in primt- 
tive forms, Connection with Oxynoticeras improbable, since the hollow keel appears to 
have arisen independently. 
Family 9. Amaltheidae. Buckman, p.p. Discoidal and involute shells, the 
young of which have fold-like costae rising into heavy nodes just inside the lines of 
involution. Costae become prominent and sharp 
at wmbilical shoulders and ventro-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); Paltoplewroceras, 
Buckm. (Plewroceras, 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 Fic. 1202. 
first, and may remain so or have a solid keel. — Amaitheus margaritatus, Montf. Middle 
Costae single, and usually bend at ventro-lateral Ae Li Eee Erodes Cea pate 
angles toward the keel, but do not cross the ventral surface. This is homologous with the 
: . . . “black layer” of Nautilus. 
venter except in late stage of Pseudotropites. 
Zurcheria, Huplopleuroceras, Dorsetensia, Buckm, ; Pseudotropites, Canav. ; Canavarites, 
eg. nov. Type C. (Ariet.) diseretum, 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 Hildoceratidae and 
Poectlomorphidae in compressed forms. Keel hollow. 
Phymatoceras, Hammatoceras, Hyatt; Lillia, Bayle; Haugia, Polyplectus, Char- 
tronia, Denckmannia, Buckm. 
The type of Phymatoceras is Amm. Tirolensis, Dumortier, the so-called P, robustum, 
Hyatt, having proved to be identical with the young of that species. Upper Lias and 
Inferior Oolite. 
Sub-Family Sonnininaz. Buckman. Sonninia includes discoidal forms 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 sides, and continued internally 
by single costae. JWVitchellia has nodes only in the young, and costae become single or 
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