Hemiphragmoceratidae is a family of endogastrically brevconic
oncocerids characterized by elaborately visored apertures in which the hyponomic sinus in mature specimens is on a spout-like process and there may be lateral and dorsal salients. (Sweet 1964, Flower 1950). Shells are compressed with the apical portion curved and the anterior straight. Siphucles are nummuloideal with expanded spheroidal segments and continuously actinosiphonate interiors.
The Hemiphragmoceratidae are probably descended from the Oncoceratidae and are known from the middle and upper
Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...
but may range into the middle
Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
(Sweet 1964). They are similar with regards to their constricted and ornate apertures to the middle Silurian exogastric Trimeroceratidae and the Siluro-devonian
discosorid Phragmoceratidae (Teichert 1964)
Some five genera have been described; ''
Hemiphragmoceras'', ''
Conradoceras'', ''
Hexameroceras'', ''
Octamerella'', and ''
Tetrameroceras''.
References
* Sweet, W. C. 1964; Nautiloidea-Oncocerida, in the Treatise on Invertebrate Paleontology; Geological Society of America and University of Kansas Press.
* Flower, R. H. and Kummel B, 1950; A Classification of the Nautiloidea; Journal of Paleontology V24 n.5 Sept 1950
* Teichert, C. 1964; Nautiloidea-Discosorida, in the Treatise on Invertebrate Paleontology; Geological Society of America and University of Kansas Press.
{{Taxonbar, from=Q16982995
Prehistoric nautiloid families
Silurian first appearances
Silurian cephalopods
Devonian cephalopods
Middle Devonian extinctions
Oncocerida