—————————— oe 
ve a agit 
199 
nearly occluded by the last. In the presence of so much 
diversity in form and structure this family is subdivided into 
three sections :— 
I Axcocuratires. Arietites and Aegoceras. 
II Harroceratites.—Harpoceras, Oppelia, Haploceras. 
TIL SrerpanoceratitEs.—Stephanoceras, Cosmoceras, Ancylo- 
ceras, Baculina, Simoceras, Perisphinctes, Olcostephanus Scaphites, 
Hoplites, Acanthoceras, Stolicakaia, Crioceras, Heteroceras, Pelto- 
eeras, Aspidoceras. 
Genus Axcocrras, Waag.—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 umbilicus; in some shells 
the ventral side is convex and enlarged, and the sides highly 
ornamented with ribs, tubercles, or elongated spines ; in other 
species the sides have simple folds or undulations, as deg. 
Jamesoni, Sow., and some are smooth, as Aeg. planorbis, Sow. 
Fic. 51.—Aegoceras capricornum, Fic. 52.—Aegoceras Davai, 
Schloth. Sow. 
The ventral side is in general round, as Aeg. capricornum, 
Scun., fig. 51, and Aeg. Davai, Sow., fig. 52; 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. angulatum, Scuu., and Aeg. Charmasset, 
p’Ors. In all the species a keel is absent, and there are no 
lateral longitudinal channels in the siphonal or ventral area. 
The body-chamber varies in length from two thirds to an 
entire whorl. The mouth-border is simple; the edge has 
