246 
THE LIAS AMMONITES. 
IV. Family. — AEGOCERATiDiE, Neumayr. 
This family includes a considerable number of Ammonite groups which have widely 
different forms and affinities, so that it is almost impossible to give a general description 
of the family which shall be correct and comprehensive at the same time. 
The lobes present a great variety of ramified figures ; the suture-line is in general 
complicated ; the siphonal lobe large, and the principal lateral and secondary laterals 
attain considerable dimensions. 
The siphonal or ventral area is in general round and well developed ; in some there 
is a keel with lateral channels more or less deeply grooved ; in others the shell is flattened 
and discoidal, with a wide open umbilicus ; or it is round and inflated, with highly involute 
whorls and a small umbilicus, sometimes nearly occluded by the last. In the presence 
of so much diversity in form and structure this family is subdivided into three sections : 
I. Aegoceratites. — Aeyoceras and Arietites. 
II. Harpoceratites. — Harpoceras, Oppelia, Haploceras. 
III. Stephanoceratites. — Stephanoceras, Cosmoceras, Ancyloceras, Baculina, Simo- 
ceras, PerispJiinctes, Olcostephanm, Scaphites, Hoplites, AcantJioceras, Stoliczlcaia, 
Crioceras, Heteroceras, Peltoceras, Aspidoceras. 
Genus Aegoceras, Waog. — The form of the shell in this genus is very variable ; it 
is flat and discoidal, with a wide umbilicus, or round and involute with a small umbili- 
cus ; in some shells the ventral side is convex and enlarged, and the sides highly orna- 
mented with ribs, tubercles, or elongated spines ; in other species the sides have simple 
folds or undulations, as Aeg. Jamesoni, Sow. (PI. XI, figs. 4 — 6) and some are smooth. 
Fig. 149. — Aegoceras capri- Fig. 150. — Aegoceras Davcei, 
cornum, Schlotli. Sow. 
as Aey. planorbis, Sow. (PI. XIV, figs. 1 — 4). The ventral side is in general round, 
as Aeg, capricornum, Schlot. (fig. 149), and Aey. Davcei, Sow. (fig. 150); sometimes it 
is grooved by a median channel, which interrupts the passage of the ribs from the right 
to the left side of the shell, as is especially the case in Aeg. angulafnm, Schlot. (PI. XIV, 
