16 



Fossil Fishes, 



enamelled scales, ornamented in some species by fine striae. From 

 the similarity of form of the dorsal spines and their mode of 

 implantation, the small and shagreen-like scales, which scarcely 

 overlap, the cartilaginous skeleton, and naked branchial arches, 

 they are considered by some ichthyologists to occupy a position 

 intermediate between the Plagiostomi and the Ganoidei. 



Fig. Z2.—Acanthodes, sp. (restored figure, after Kner and Roemer), Permian. 



They are represented by Biplacanthus (Fig. 31), Cheir acanthus, 

 CUmatius, Euth acanthus, and Parexus, from the Old Red Sandstone, 

 and Acanthodes (Fig. 32), ranging from the Old Red to the Permian. 



Wall-case, 

 No. 4. 



Group II. — Placodermata. 



The Placodermata are characteristic of the Old Red Sandstone 

 or Devonian rocks. The head and anterior portion of the body 

 were covered with large bony plates, sculptured and ornamented 

 with beads of enamel. 



In the genus Pterichthys (Figs. 33 and 34) there are two peculiar 

 arms, or anterior fins, articulated to the sides of the body, just 

 behind the head ; the tail is covered with scales, and supports the 

 dorsal fin. 



The gigantic Asterolepis seems to have been allied to Pterichthys. 



In Coccosteus (Figs. 35 and 36) the tail was destitute of scales, 

 but very distinct neural and haemal spines are seen with interspinous 

 bones, supporting a dorsal and anal fin ; no vertebra? have been 

 observed, so that the notochorcl must have been persistent. 



Prof. Newberry has described a huge Placoderm (Dinichthys) 

 from the Devonian of North America, the dentition of which greatly 

 resembles that of the recent Protopterus (Fig. 37). Dr. Traquair 

 is of opinion that the Placodermata may turn out to have been an 

 aberrant group of loricated Dipnoi, while Prof. Cope has recently 

 suggested that the Pterichtliyidcc, at least, are not fishes, but an 

 ancient order of Tunicates. 



