CEPHALOPODA 



601 



Pledoceras Hyatt. Ordovician and Silurian. Sphyradoceras Hyatt {Peismoceras, 



Systrophoceras Hyatt) (Fig. _ 



1114). Silurian and 



Devonian. The first is gyro- 

 ceraconic, with some discoidal 

 nautilicones, and the second is 

 almost exclusively torticonic 

 of tlie trochoceran type. 



Family 7. Ophidio- 

 oeratidae Hyatt. 



Discoidal nautilicones^ 

 costated from the neanic stage 

 onward. Volutions of the 

 young small and numerous. 

 Section during the ephebic stage 

 generally compressed, venter 

 narrower than the dorsum. 

 Siphuncle tubulär, small. 



Fi«. 1114. 



Sphymdoceras optaUim (Barrande). Silurian 

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



the young. 



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, biit ventrad during the nepionic. 

 Gerontic apertures with prominent dorsal 

 and lateral crests, and very deep hypo- 

 nomic sinus. Silurian. 



Homaloceras Whiteaves. Cyrtocera- 

 cönes with section similar to that of Ophi- 

 dioceras, venter narrow and channelled, 

 bordered by crenulated ridges ; the dorsum 

 gibbous and rounded. Siphuncle near 

 the venter. Devonian. 



Family 8. Lituitidae Noetling. 



Ophidioceras simpUx Barr, 

 Silurian (Etage B); Lochkow, 

 Bohemia. i/i (after Barrande). 



Excepting the supposed ancestral, 

 primitive genus, Gyclolituites, this is a 

 series of phylogerontic uncoiled forms with 

 an extreme modification in the almost 

 completely uncoiled Rhynchorthoceras. 

 Apertures quite distinct from those of the preceding family ; hyponomic 

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

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

 and five crests. Biphuncle tubulär and usually largc. 



Fio. 1116. 



Lituites lituus 

 Montf. Ordovician 

 drift ; East Prussia. 

 1/2 (after Noetling). 

 Gyclolituites Remele ; Lituites Breyn {Fig. 1116); Angelinoceras, 



Holmiceras Hyatt. Ordovician. Ancistroceras Boll, and Rhynchorthoceras Remele. 



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



