432 



MESOZOIC ERA— AGE OF REPTILES. 



then the curved Gyroceras, then the coiled Nautiloids, then the simple 

 suture became angled in Goniatite, then scalloped in Ceratite, and 

 finally complexly frilled in Ammonite. It is remarkable, however, that 

 one of the simpler forms, viz., the nautiloids, although also one of the 

 earliest, has outlived them all. The corresponding figures on the left 

 are sections showing the position of the siphuncle. 



The order in which these several genera appeared, and their contin- 

 uance, are shown in the diagram (Fig. 669) on page 434. 



Belemnites. — The Belemnite (/3eAe/xvov, a dart) was nearly allied to 

 the squid and cuttle-fish of the present day. Like the squid, it had an 



internal bone (the pen of the 

 squid), except that the bone is 

 much larger and heavier in the 

 Belemnite. It is this bone, or 

 the lower portion of it, which is 

 usually fossilized (Figs. 664-667). 

 When perfect it is expanded and 

 hollow at the upper end, and in 

 the hollow is a small, conical, 



Fig. 660. Fig. 661. Fig. 662. 



Figs. 660-662.— 660. Internal Shell of Belemnite (restored by D'Orbigny). 661. The Animal (restored 

 by Owen). 662. A living Sepia for comparison. 



chambered, siphuncled shell, the Phragmocone. Fig. 660, a and #, 

 shows the perfect bone, and Fig. 664 the upper part broken and the 

 phragmocone in place. Like the squid, too, it had an ink-bag, from 

 which it doubtless squirted the inky fluid to darken the water and 



