Trimeroceratidae

Reconstruction of Pentameroceras mirum, by Avancna.

Belongs within: Oncoceratidae.

The Middle Silurian Trimeroceratidae resembled the related Hemiphragmoceratidae in having the shell aperture visored by encroaching lappets. The two families mainly differed in the structure of the siphuncle, that of Trimeroceratidae being slender and without actinosiphonate deposits.

Characters (from Sweet 1964): Exogastric, mostly compressed brevicones with slender, empty siphuncles. Aperture visored; mature peristome with median dorsal sinus.

<==Trimeroceratidae
    |--Clathroceras Foerste 1926 S64
    |    `--*C. sulcatum (Barrande 1865) [=Phragmoceras sulcatum] S64
    |--Eotrimeroceras Foerste 1928 S64
    |    `--*E. jupiterense Foerste 1928 S64
    |--Pentameroceras Hyatt 1884 S64
    |    `--*P. mirum (Barrande 1865) [=Gomphoceras mirum] S64
    |--Trimeroceras Hyatt 1884 S64
    |    |--*T. staurostoma (Barrande 1865) [=Gomphoceras staurostoma] S64
    |    `--T. gilberti Kindle & Breger 1904
    |--Inversoceras Hedström 1917 S64
    |    |--*I. perversum (Barrande 1865) S64 [=Phragmoceras perversum S64; incl. I. constrictum T64]
    |    `--I. percurvatum [incl. I. barrandei] T64
    `--Stenogomphoceras Foerste 1930 S64
         |--*S. chadwicki Foerste 1930 S64
         |--S. contractum Foerste 1930 P68
         |--S. gracile Foerste 1930 P68
         `--S. inflatum Foerste 1930 P68

*Type species of generic name indicated

REFERENCES

[P68] Purnell, L. R. 1968. Catalog of the Type Specimens of Invertebrate Fossils. Part I: Paleozoic Cephalopoda. United States National Museum Bulletin 262: 1-198.

[S64] Sweet, W. C. 1964. Nautiloidea – Oncocerida. In Treatise on Invertebrate Paleontology pt. K. Mollusca 3. Cephalopoda – General Features – Endoceratoidea – Actinoceratoidea – Nautiloidea – Bactritoidea (R. C. Moore, ed.) pp. K277-K319. The Geological Society of America and the University of Kansas Press.

[T64] Teichert, C. 1964. Morphology of hard parts. In Treatise on Invertebrate Paleontology pt. K. Mollusca 3. Cephalopoda – General Features – Endoceratoidea – Actinoceratoidea – Nautiloidea – Bactritoidea (R. C. Moore, ed.) pp. K13-K53. The Geological Society of America and the University of Kansas Press.