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The suture includes a ventral saddle and broad lateral lobes. In some, there is a secondary ventral lobe. The siphuncle is subcentral. Juvavionautilus comes from Europe and Timur. Oxynautilus, [5] differs from the rest in that it has an involute, compressed lenticular shell with a narrow or acute (angular) venter which may or may not have a ...
Gryponautilus from the Upper Triassic is broadly involute with a narrowly rounded, keel-like venter at maturity and shallow ventral and lateral lobes in the suture. All members of the Grypoceratidae have a ventral lobe with the exception of Stenoporceras, Parastenopoceras, and Virgaloceras, which have a ventral saddle instead. The derivation of ...
The Gonionautilidae, named by Kummel in 1950 to contain the Upper Triassic genus Gonionautilus, have a smooth, involute, compressed shell with narrow flattened venter and a suture like that of Clydonautilus, but with a more highly developed median saddle and double-pointed annular lobes.
The suture is with ventral and dorsal lobes, the siphuncle very close to the venter. Carlloceras has a moderately involute shell with a compressed trapezoidal whorl section, nearly flat ventral and lateral areas, and slight dorsal impression. The suture has a ventral saddle and broad lateral lobe and the siphuncle is small and near the venter.
The external or ventral region refers to sutures along the lower (outer) edge of the shell, where the left and right suture lines meet. The external (or ventral) saddle, when present, lies directly on the lower midline of the shell. As a result, it is often called the median saddle. On suture diagrams the median saddle is supplied with an arrow ...
The shell of Proclydonautilus, like those of other Clydonautilitidae, is involute and smooth. It is distinguished by its suture which has a broad, shallow to deep ventral lobe that divides a large ventral saddle. A large lateral lobe on the flans is followed by a small lateral saddle and a second lateral lobe.
Pseudonautilus: Shell involute, compressed; whorl section higher than wide, flanks flattened; venter broadly arched; umbilicus small and deep; suture with deep narrow ventral lobe, large V-shaped lateral lobes on either side followed by rounded saddles then smaller lobes just above the umbilical seam; siphuncle subventral. Found in Europe and ...
The shell of Aturia is rounded ventrally and flattened laterally; the dorsum is deeply impressed. The suture, one of the most complex in the Nautiloidea , has a broad flattened ventral saddle, narrow pointed lateral lobes, broad rounded lateral saddles, broad lobes on the dorso-umbilical slopes, and a broad dorsal saddle divided by a deep ...
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