CLASS V 



CEPHALOPODA 



601 



Pledoceras Hyatt. 



Ordovician and Silurian. Sphyradoceras Hyatt (Peismoceras, 

 Hystrofhoceras Hyatt) (Fig. 

 1114). Silurian and 



Devonian. The first is gyro- 

 ceraconic, with some discoidal 

 nautilicones, and the second is 

 almost exclusively torticonic 

 of the trochoceran type. 



Family 7. Ophidio- 

 ceratidae Hyatt. 



Discoidal nautilicones, 

 costated from the neanic stage 

 onioard. Volutions of the 

 yoicng small and numerous. 

 Section during the ephebic stage 

 generally compressed, venter 

 narrower than the dorsum. 

 Siphuncle tubular, small. 



Ophidioceras Barr. (Fig. 

 1115). Nautilicones with 

 straight lateral costae and 

 raised bands on the venter, 

 and longitudinal ridges in 

 Siphuncle dorsad or ventrad of centre during ephebic 

 stage, but ventrad during the nepionic. 

 Gerontic apertures with prominent dorsal 

 and lateral crests, and very deep hypo- 

 nomic sinus. Silurian. 



Homaloceras Whiteaves. Cyrtocera- 

 cones with section similar to that of Oj^hi- 

 dioceras, venter narrow and channelled, 

 bordered by creniilated ridges ; the dorsum 

 gibbous aiid rounded. Siphuncle near 

 the venter. Devonian. 



Viv.. 1114. 

 f 



Sphyradoceras optatum (Barrande). Silurian 



(Etage E) ; Loclikow, Bohemia (after Barrande) 



the young. 



Family 8. Lituitidae Noetling. 



Excepting the supposed ancestral, 

 primitive genus, Cyclolituites, this is a 

 series of phylogerontic uncoiled forms with 

 an extreme modification in the almost 

 completely uncoiled Bhynchorthoceras. 

 Apertures quite distinct from those of the preceding family ; hyponomic 

 sinus shallower, there are narrow ventro-lateral crests, and small lateral 

 sinuses and crests, some forms having altogether as many as five sinuses 

 and five crests. Siphuncle tubular and usually large. 



Fii;. 1115. 



Ophidioceras simplex Barr. 

 Silurian (Etage E) ; Loclilcow, 

 Boliemia. i/i (after Barrande). 





Pig. 1116. 



Lituites lituus 

 Montf. Ordovician 

 drift ; East Prussia. 

 1/.J (after Noetling). 



Cyclolituites Remele ; Lituites Bveyn {Fig. 1116); Angelinoceras. 

 Holmiceras Hyatt. Ordovician. '^i^?ictsiroceras Boll, and Bhynchorthoceras Remele 

 Ordovician and Silurian. (For re-descriptions see Hyatt's Phytogeny, 1894.) 



