524 MOLLUSCA SUB-KINGDOM VI 
more rapidly into nodose or symmetrical, spout-like, spinous processes. More specialised 
forms are tuberculated as in Ryticeratida, but there are never more than three rows of 
nodes on either side, and these are regularly distributed—one on the wmbilical shoulder, 
another on the ventro-lateral angle, and the third close to the median ventral line. 
Annular lobes absent except in a few Triassic forms. Siphuncle generally more or less 
nummulordal. 
Family 17. Hercoceratidae. 
Cyrtoceracones, gyroceracones, nautilicones, and torticones having depressed elliptical, 
sub-quadrate, or trapezoidal sections. Aperture has two deep sinuses with projecting edges 
at the ventro-lateral angles, and these are usually persistent, forming two lines of more or 

Ptenoceras (Gyr.) alatum, 
re. 1071. Barr. sp. Silurian (F); 
Hercoceras mirum, Barr. Silurian (Btage G); Hlubocep, Bohemia (after Konieprus, Bohemia.  1/) 
Barrande). (after Barrande). 
less spout-like processes. Sutures with ventral, lateral, and dorsal lobes. Siphunele 
ventrad of centre. 
Hercoceras, Barr. (Fig. 1071); Trochoceras, Barr.; Ptyssoceras, Ptenoceras (Fig. 
1072), Anomaloceras, Hyatt. Silurian. 
Family 18. Tainoceratidae. 
‘ Discoidal nautilicones with more or less massive volutions which at some stage or 
throughout life are trapezoidal in section, tuberculated, and without well-defined lateral 
and umbilical zones. Sutures have ventral, lateral, and dorsal, but no annular lobes, 
Spinous processes are complete, never spout-like. Siphuncle small, tubular, 
Temnocheilus, M‘Coy (Endolobus, Meek ; Cryptoceras, d’Orb.). Section trapezoidal 
throughout life, and one row of persistent spines and nodes on either side at the 
ventro-lateral angles. Devonian to Carboniferous. 
Foordiceras, Hyatt. Permian. Metacoceras, Coelogasteroceras, Hyatt.’ Carbon- 
iferous. Diadiploceras, Hyatt: Devonian. Tainoceras, Hyatt. Carboniferous. 
Family 19. Centroceratidae. § 
Gyroceracones and nautilicones with young similar to early stages of Temnocheilus 
before the impressed zone is formed. Shell subsequently becoming tetragonal in section, 
es 
