""'Mecynoceras " "'is a Late Devonian oncocerid included in the Poterioceratidae, a family of subcircular to compressed exogastric cyrtocones without a hyponomic sinus.
22.
The peristome ( aperture rim ) has a broad hyponomic sinus-for the hydrojet funnel, ventrolateral projections, dorsolateral sinuses-possibly for the eyes, and probably a mid dorsal sinus.
23.
"Grimsbyoceras ", named by Foerste in 1926, has a depressed, breviconic shell, with an elliptical transverse aperture, without a hyponomic sinus, and a small, subventral siphuncle.
24.
The narrow hyponomic sinus, which is an opening for the water-jet funnel by which the animal could move, much as with modern squid and octopods, points toward the lower or ventral side.
25.
The body chamber of " Stradoceras " is straighter and more slender than the chambered phragmocone; the venter narrowly rounded with a shallow hyponomic sinus; the aperture open, sutures with shallow lateral lobes.
26.
The aperture, which is constricted, consists of a narrow, vertical slit-like opening extending from the ventral hyponomic sinus to a dorsal sinus and two pairs of lateral sinuses that diverge in the upper portion.
27.
The juvenile spiral portion has a deep indentation on the ventral side of the aperture for the water-jet funnel, known as a hyponomic sinus, that becomes broad and shallow in the straight-shelled adult portion.
28.
"Eutrephoceras " is generally subglobular, broadly rounded laterally and ventrally, with a small to occluded umbilicus, broadly rounded hyponomic sinus, only slightly sinuous sutures, and a small siphuncle that is variable in position.
29.
Ascoceratinae have an exogastric ascoceroid stage characterized by the development of a protruding neck ending at the aperture, both ocular and hyponomic sinuses which form when fully grown, and camerae that are mostly confined to the dorsal half of the shell.
30.
Flower 1943 : rapidly expanding, apically curved, adorally straight, faintly compressed with ovoid cross section; sutures straight, slightly oblique; exterior with transverse bands and fine longitudinal markings; no hyponomic sinus; siphuncle small, ventral . " M Ord"
