AMMONITID&. i 
Amalthec. 
Shell generally flattened and carinated, the last whorl of the 
spire covering a large part of the preceding; sutural line with 
several auxiliary lobes. Aptychus simple, corneous, only known 
in the Jurassic forms. 
AMALTHEUS, Montfort, 1808. 
Distr.—68 species. Triassic, Jurassic and Cretaceous. A. 
margaritatus, d’Orb. (xxxviii, 26, 27). 
Periphery sharpened or carinate; ribs when present, absent 
at this part or broken up into tubercles or folds; the geologi- 
cally older forms with spiral strie on the external layer of the 
shell, which corresponds to the wrinkled layer of the Arceste. 
Body-chamber short, one-half to two-thirds of a whorl long ; 
margin of aperture simply emarginate, with long, external pro- 
cesses, ending in spoon-shaped extremities, sometimes bent out- 
wards or inwards. Lobes usually strongly incised, siphonal 
lobe shorter than the first lateral, lobular bodies broadly wedge- 
shape. Umbilicus open, with the sides of the whorls exposed 
or only partially covered. 
PLEUROCERAS, Hyatt, 1868. (Prionotropis, Meek, 1876.) Per- 
iphery flat, with keel and channels well defined ; keel crenulated ; 
channels vary from obsolete to deep and well-defined, pile 
swelling below, tuberculated ; genicular bend prominent. Tuber- 
cles lateral, arranged along the line of envelopment. Umbilicus 
open. Ventral lobe narrow and but slightly deeper than the 
lateral lobes; the latter unequally divided. Inferior lateral lobe 
small, shallow, equally divided. Superior lateral cell only partly 
exposed on the side, and together with the inferior lateral, 
unequally divided. Scarcely distinct from Amaltheus. Middle 
Lias, Cretaceous. A. spinatus, Brug. (xxxviii, 24,25). A. (Prio- 
notropis) Woolgari, Mantell (xxxvii, 10, 11). 
OXYNOTICERAS, Hyatt, 1874. Periphery carinated in the young 
shell, rounded in the adult. A. Guibalianus, W’Orb. (xl, 50, 51). 
Lower Lias. 
PTYCHITES, Mojs.,1875. Shell covered with undulated radiating 
plications; exterior lobe shallow; exterior saddle but little 
elevated ; first lateral saddle very high; saddles dentate or 
slightly branched. This group, which corresponds to the Plicosi 
of Beyrich and the Rugiferi of Oppel, may be considered an 
ancestral form of Amaltheus. Six Triassic species. A. Studeri, 
Hauer. 
ScHLOENBACHIA, Neumayr, 1875. 
Dedicated to the geologist, Schloenbach. 
Syn.—Mortoniceras, Meek, 1876. 
Distr.—46 species. Cretaceous; Europe and United States. 
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