76 



CEPHALOPODA. 



the siplmncle. The known species range from the Lower 



Silurian to the Devonian. 



Goniatites and Badritcs are sometimes raised to the rank 



of a distinct sub-family {Goniatitidcc), and many palaeontolo- 

 gists place Clymcnia along mth them. 

 As regards its development, Goniatites 

 is shown to belong to the Ammon- 

 ifidcc by its possession of an inflated 

 ■'ovisac" or embryonic shell {see fig. 

 450), but its simply-lobed septa separ- 

 ate it from the true Ammonites, of 

 which it is an ancient and compara- 

 tively simple representative. 



Fig. 462. — Goniatites {Aganides) Jossce. Carboniferous 



The genus Ceratites (fig. 463) comprises forms which re- 

 semble Goniatites in having a discoidal shell, the coils of 

 which lie in one plane and are contiguous. It is distin- 

 guished, however, from Goniatites on the one hand and 

 Ammonites on the other, by ha\dng the " lobes " of the 

 suture denticulated or crenulated, whilst the " saddles " are 

 simply rounded. The species of Ceratites are typically 

 Triassic, the best -known form being the C. nodosv.s of the 

 Muschelkalk. Some species, however, occur in the Creta- 



