964 



CLASS PISCES. 



ae -jirnx 



Family Coccosteid^e. — The genus Coccosteus differs so markedly 

 from the members of the preceding family that Dr Traquair has sug- 

 gested that it should form the type 

 of a distinct suborder. The head 

 has distinct bones and plates differ- 

 ing markedly in their arrangement 

 from those of the preceding family, 

 but their structure has only re- 

 cently been rightly explained (fig. 

 894). In the restoration given 

 by Agassiz (fig. 895), although the 

 arrangement of the posterior plates 

 is fairly correct, yet anteriorly the 

 grooves of the lateral line were 

 mistaken for sutures ; while the 

 ethmoidal bones at the muzzle 

 and the orbital notches are omit- 

 ted. An approximation to a cor- 

 rect restoration of the lateral aspect 

 is shown in fig. 896, but the mouth is made too long. The cara- 

 pace, or body-shield, consists of a long shield-shaped middle dorsal 

 plate, flanked by lateral plates, and completed by a median ventral 

 plate. The posterior half of the body is totally unprotected, but 

 interspinous bones in the vertebral column support an anal and a 



Fig. 894. — Dorsal aspect of the cranium of 

 Coccosteus decipiens ; from the Devonian of 

 Scotland. ae, Ethmoidal, with nares of 

 either side; p.m.x, Premaxilla ; p.o, Preor- 

 bital, external to which is the orbit ; fit.o, 

 Postorbital ; c, Central, m, Marginal, n, 

 Middle occipital; e.n, Lateral do. (After 

 Traquair.) 





Fig. 805. — Dorsal view of Coccosteus decipiens, as restored by Agassiz. In the anterior part 

 of the head the ethmoids and orbits have been omitted, and the black lines mostly indicate the 

 grooves of the lateral line system, and not sutures. The shield-shaped plate immediately behind 

 the skull is the middle dorsal, in advance of which is the middle occipital of the skull. 



dorsal fin. There appears to have been no pectoral fin, although 

 certain forms which have been generically or subgenerically separ- 

 ated as Brachydirus have been represented with such an appendage. 

 Both this and the next genus are characteristic of the Devonian, 

 Coccosteus being common to Europe and Canada. The allied Homos- 

 teus includes gigantic forms from Scotland and the Eifel, readily 

 distinguished by the form of the cranial and body plates. Thus 

 the middle occipital plate is longer and narrower, and the middle 

 dorsal wider than long, and not pointed behind. Professor Huxley 



