604 



MOLLUSCA 



PHYLUM VI 



Shells ivith longitudinal ridges and sometimes annular folds in the young, hut often 

 smooth in the epliehic stage. Sutures with ventral, lateral^and dorsal lobes, or almost 

 straight. Siphunde nummxdoidal and often dorsad of centre. Annular lobes knoion to 

 be present in specialised forms. 



Bhadinoceras, Nephriticeras Hyatt. Devonian. 



Family 14. Trigoiioceratidae Hyatt. 



Gyroceracones and nautilicones having at some stage or throughout life trigonal 

 volutions, a more or less concave venter, and generally fluted shell. Sidures 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 roiujhened by transverse 

 bands as in Thoracoceras. Siphunde small, ventrad of centre. 



Trigonoceras M'Coy ; Goelonautilus Foord {Trematodiscus Meek; Trematoceras 



Hyatt) ; Subclymenia d'Orb. ; Stroboceras, 

 Apheleceras, Diorugoceras, Ephippioceras 

 © v Hyatt. Carboniferous. All nautilicones 



but the first, wliicb is gyroceraconic. 



Family 15. Triboloceratidae Hyatt. 



Gyroceracones and nautilicones similar 

 to Trigonoceratidae, and with concave 

 venter at an early stage or until late in 

 life. The venter afterioards becomes more 

 or less elevated, and in most species convex. 

 Sutures also similar, but annular lobes 

 are present in all the nautilicones save 

 Goloceras. 



Fi(i. 1119. 



Vest i nautilus kcinincli (d'Orb.). Lower Carboniferous ; 

 Tournay, Belgium. Oral and lateral aspects of young 

 individual, with umbilical perforation. 



Triboloceras Hyatt; Vestinautilus Ryckh. (Fig. 1119); Planetoceras, Stearoceras, 

 Goloceras Hyatt. Carboniferous. 



Family 16. Rhineceratidae Hyatt. 



Gyroceracones and nautilicones like Tlioracoceras in nepionic stage, but subsequently 

 becoming biangular in section, and generally developiing solid, more or less tetragonal, 

 volutions. Longitudinal ridges and flutes also developed, but are more uniform in size 

 than in the preceding family, and venter is always convex. Annular lobes present in 

 all nautilicones so far as hnoivn. 



Rhineceras, Lispoceras, Thrincoceras, Phloioceras, Discitoceras {Discites ]\I'Coy), 

 Leuroceras, Phacoceras Hyatt. Carboniferous. 



VI. Hercoceratida Hyatt. 



Primitive shells have projecting bands of groivth and p)rocesses similar to those of 

 primitive Ryticeratida, but less numerous, being present in only one row, and evolving 

 more rapidly into nodose or symmetrical, spout-lilce, spinous processes. More sp>ecialised 

 forms are t-uherculated as in Ryticeratida, but there are never more than three rows of 

 nodes on either side, and these are regularly distributed — one on the umbilical shoulder, 

 another on the ventro -lateral angle, and the third close to the median ventral line. 



