CLASS V CEPHALOPODA 599 



Protobactrites Hyatt. Long pencil-sliajied orthoceracones and cyrtoceracones, 



(hthocerasinterm,ediumMa,Tk\m. Silurian ; 

 Gottland. Longitudinal section showing 

 siiiliuncle, si^pta and pseudosepta ; cainerae 

 lilled up vvitli calcite. 



Fio. 1110. 



Orthocrras michclini 

 Barr. Silurian ; Kozorz, 

 Bohemia. Longitudinal 

 section showing short 

 siiilioual funnels. 



circular, or compressed ellii)tical in section, ornamented with 

 transverse and sometimes longitudinal striae. Si])huncle 

 tubular, centren or near the centre. Truncation occurs in some 

 species, and others are more or less transitional to Bactrites 



among the Ammonoids. 

 ceras) styloid eum (Barr.). 

 boniferous. 



Type P. {Ortho- 

 Silurian to Car- 



Family 2. Cycloceratidae Hyatt. 



Fig. 1111. 



Geiaonoceras timidum 

 (Barr.). Silurian ; Loch- 

 kow, Bohemia. 



Fio. 1112. 



Daicsonocrras annula- 

 twill (Sowb.). Silurian 

 (Etage B) ; Viscocilka, 

 Bohemia. Terminal por- 

 tion showing shell of 

 living chamber and 

 sectioned canierae (after 

 Barrande). 



Orthoceracones and cyrtoceracones having annuli with transverse 

 sfridje or hands of grototh at all stages ; longitudinal ridges, when 

 present, more or less discontinuous. The earliest forms often have 

 large siphuncles, and are apparently more directly connected ivith 

 primitive Endoceratida than with the Orthoceratidae. 



Protocycloceras Hyatt. Annulated orthoceracones and cyrto- 

 ceracones without longitudinal ridges. Siphuncle large. Type 

 P. (Orthoceras) lamarcki (Bill.). Ordovician. 



Gy cheer as M'Coy (Dictyoceras, Heloceras Eichw.). Annulated 

 orthoceracones and cyrtoceracones with discontinuous longitudinal 

 ridges. Siphuncle generally tubular or with fusiform segments ; 

 deposits when jaresent irregular as in Orthoceras. Annuli often 

 become obsolete in paragerontic stages. Ordovician to Permian. 



Dawsonoceras Hyatt (Fig. 1112). Similar to Cycloceras, but 

 liaving prominent frilled bands of growth between and on the 

 annulations, the frills sometimes forming more or less discon- 

 tinuous longitudinal ridges. Silurian and Devonian. 



Ctenoceras Noetling. Cyrtoceracones like Dawsonoceras dulce 

 (Barrande), but with fine longitudinal ridges between the annuli, 

 and living chamber with three internal folds or processes — one 

 median dorsan, and a pair on the A^enter. Siphuncle dorsad of 

 centre. Oidovician. 



Family 3. Kionoceratidae Hyatt. 

 Orthoceracones and cyrtoceracones with more or less well-marked continuous longi- 



