THE CARBONIFEROUS PERIOD. 



187 



With lobed or aiigulated septa, and a dorsally-placed siphuncle 

 (situated on the convex side of the curved shells), now for the 

 first time commences to acquire a considerable prominence. 

 The principal representative of this group is the genus Gonia- 

 tites (fig. 129), which commenced its existence in the Upper 

 Silurian, is well represented in the De- 

 vonian, and attains its maximum here. 

 In this genus, the shell is spirally 

 curved, the septa are strongly lobed 

 or angulated, though not elaborately 

 frilled as in the Ammonites, and the 

 siphuncle is dorsal. In addition to 

 Go7iiatites^ the shells of true Ammon- 

 ites, so characteristic of the Secondary 

 period, have been described by Dr 

 Waagen as occurring in the Carbon- 

 iferous rocks of India. 



Fig. 129. — Goniatites {Aganides) Josste. Carboniferous Limestone. 



Coming finally to the Verfebrata, we have in the first place 

 to very briefly consider the Carboniferous fishes. These are 

 numerous ; but, with the exception of the still dubious " Cono- 

 donts," belong wholly to the groups of the Ganoids and the 

 Placoids (including under the former head remains which per- 

 haps are truly referable to the group of the Dipnoi or Mud- 

 fishes). Amongst the Ganoids, the singular buckler-headed 

 fishes of the Upper Silurian and Devonian {Cephalaspidce) have 



