SUB-ORDER D ORTHOCHOANITES 523 
Family 13. Rhadinoceratidae. 
Primitive discoidal gyroceracones and nautilicones with stowt volutions, circular or 
depressed elliptical in section, but becoming reniform in later stages of nautilicones. 
Shells with longitudinal ridges and sometimes annular folds in the young, but often 
smooth in ephebic stage. Sutures with ventral, lateral, and dorsal lobes, or almost 
straight. Siphuncle nummuloidal and often dorsad of centre. Annular lobes known to 
be present in specialised forms, 
Rhadinoceras, Nephriticeras, Hyatt. Devonian. 
Family 14. Trigonoceratidae. 
Gyroceracones and nautilicones having at some stage or throughout life trigonal 
volutions, a more or less concave venter, and generally fluted shell. Sutures with ventral 
saddles in the young, becoming divided by shallow lobes in later stages, and in some genera 
the dorsal lobes of the young become divided subsequently by dorsal saddles. Gerontic 
living chamber occasionally free near the aperture. Annular lobes observed in only one 
species (Apheleceras disciforme). Young have longitudinal ridges roughened by transverse 
bands as in Thoracoceras. Siphuncle small, ventrad of centre. 
Trigonoceras, M‘Coy ; Coelonautilus, Foord (Trematodiscus, Meek ; Trematoceras, 
Hyatt) ; Subclymenia, V’Orb. ; Stroboceras, 
Apheleceras, Diorugoceras, Ephippioceras, 
Hyatt. Carboniferous. All nautilicones 
but the first, which is gyroceraconic. 
Family 15. Triboloceratidae. 
Gyroceracones and nautilicones similar 
to Trigonoceratidae, and with concave 
venter at an early stage or wntil late in 
life. The venter afterwards becomes more 
or less elevated, and in most species convex. Fie. 1070. 
Sutures also siumilar, but annular lobes — Vestinautilus Konincki, WVOrb. sp. Carboniferous 
ey a ; A ahs e@ ea7 Limestone; Tournay, Belgium. Oral and_ lateral 
IT es i } j e e ? ere a cts : 
ny Coe resent im all the nautilcones save aspects of young individual, with umbilical perforation. 
Coloceras. 
Triboloceras, Hyatt ; Vestinautilus, Ryckh. (Fig. 1070); Planetoceras, Stearoceras, 
Coloceras, Hyatt. Carboniferous. 

Family 16. Rhineceratidae. 
Gyroceracones and nautilicones like Thoracoceras in nepionic stage, but subsequently 
becoming biangular in section, and generally developing solid, more or less tetragonal 
volutions. Longitudinal ridges and flutes also developed, but more uniform in size than 
in the preceding family, and venter always convex. Annular lobes present in all 
nautilicones so far as known. 
Rhineceras, Lispoceras, Thrincoceras, Phloioceras, Discitoceras (Discites, M‘Coy), 
Lewroceras, Phacoceras, Hyatt. Carboniferous. 
VI. HeRcOcERATIDA. 
Primitive shells have projecting bands of growth and processes similar to those of 
primitive Ryticeratida, but less numerous, being present in only one row, and evolving 
