Curvature is exogastric, meaning the lower, or ventral, side is convex in longitudinal profile.
12.
The Oncocerids also appear during this time; they are restricted to shallow water and have short exogastric conchs.
13.
Variations include annulate orthoconic longicones, exogastric breviconic cyrtocones, forms with thin connecting rings, and those with subcentral siphuncle.
14.
"Parakionoceras " has a long, faintly curved, exogastric shell with relatively long camerae and straight transverse sutures.
15.
"Reedsoceras " was named as a genus characterized by rapidly expanding exogastric cyrtocones with unconstricted apertures and straight sutures.
16.
The straight or slightly upwardly curved, exogastric shells with weighted ventral siphuncles indicate a normal horizontal orientation with the aperture facing forward.
17.
The shell is laterally compressed, upwardly curved, and short; an exogastric brevicone with the venter narrowly and dorsum broadly rounded.
18.
The siphuncle, which is proportionally naarrow, is on the outer, concave curvature of the shell, suggesting it is exogastric.
19.
As with the ascleistoceratids, the curvature is exogastric, such that the lower side, or venter, is on the outside curve.
20.
The adult, or mature ascoceroid conch, as it is referred to, consists typically of an expanded exogastric brevicone with special unique features.
