1The straight shell typical of early nautiloid cephalopods.
〔古生物〕鹦鹉螺（模式种）
Example sentencesExamples
An orthocone is a usually long straight shell of a nautiloid cephalopod.
Long straight slender smooth orthocones, similar internally to the Ellesmeroceratidae, developing broader cross section and a thin marginal siphuncle which may be somewhat separated from the ventral wall.
1.1A fossil cephalopod with an orthocone shell.
鹦鹉螺化石
Example sentencesExamples
This single specimen is unlike all the other embryologic orthocones, but we do not believe at this time that this single individual is sufficient to erect a new species.
The group continued right until the end of the Permian or - depending on the identification of the Triassic orthocones - the end of the Triassic.
These latter orthocone ammonites do not modify the terminal body chamber, which cannot function as a floating egg-case.
Derivatives
orthoconic
adjective
Other molluscs are present but less common, including bivalves, scaphopods, orthoconic cephalopods, tentaculitids, and small, indeterminate juvenile ammonoids.
Example sentencesExamples
Cephalopod mollusks such as the orthoconic nautiloids patrolled the benthos, in a role as the main macrophagous predator.
Riccardi & Sabattini described Sueroceras, an orthoconic form with reticulate ornament, from the Late Carboniferous of Patagonia.
The apical end is missing, although the remainder of the conch suggests that its shape is orthoconic, and the apical angle may be inferred as being about 15 [degrees].
Conch orthoconic with depressed triangular cross-section; both dorsum and venter of shell with longitudinal ribs, and ventral internal mold smooth.
They were a diverse group, including both short and straight orthoconic (long-shelled) sometimes nearly cylindrical shelled forms.