THE CEPHALOPODA 157 



cessation of growth, after which renewed growth went 

 on rapidly for half a whorl when another constriction was 

 formed. 



Most specimens preserve the shell, but even where it 

 is chipped away no suture-lines can be seen. This is 

 because the body-chamber was over a whorl in length : 

 only on the inner whorls of broken specimens can the 

 suture-line be seen (Fig. 47, d). It resembles that of 

 Tornoceras in having a lateral lobe and saddle, but the 

 lobe is pointed instead of rounded ; while the external 

 is divided by a median saddle which is much more 

 prominent than that of Manticoceras retrorsum. 



These three Palaeozoic species are conveniently 

 described as "goniatites," being characterized by suture- 

 lines with simple lobes and saddles. 



FIG. 45. APERTURAL MARGINS OF CEPHALOPODA (continued) 



tudinal ornament, a', Peripheral view, showing hyponomic sinus 

 (N.S.) (After Foord and Crick. ) b, Ophidioceras simplex Barrande, 

 Silurian, Lochkow, Bohemia, b. Side view, showing ophiocone finally un- 

 coiling, and aperture with hyponomic sinus (//. S.). b' , Peripheral view ; 

 b", aperiural view. (After Barrande.) c, Arcestes distinctus(G\Q\)e\), 

 Noric (Alpine Trias). Sphserocone ; no distinct hyponomic sinus, 

 rostrum, or lappets. ( After Quenstedt.) d,d',Protrachyceras archelaus 

 (Laube), Ladinic (Alpine Trias). Apertural region, showing broad 

 rostrum. (After Mojsisovics. e, Paltopleuroceras pseudocostatum 

 (Hyatt), Domerian (Middle Lias). Long crenulate rostrum. (After 

 Quenstedt.) /",/', Pleydellia subcompta (Qranco), Yeovilian. Showing 

 relation of radial line to apertural margin. (After Buckman.) 

 g, g', Reineckia exstincta (Quenstedt), Vesulian. Showing tendency 

 to constriction of aperture, absence of distinct rostrum and lappets, 

 and relation of radial line to apertural margin. (After Quenstedt.) 

 h, h' , Brasilia effricata S. Buckman, Aalenian, Bradford Abbas, Dorset. 

 Showing very broad rostrum, no definite lappets, and relation of radial 

 line to apertural margin. (After Buckman. ) (AllxJ.) H. S., Hypo- 

 nomic sinus ; L, lappet ; R, rostrum. 



