FOSSIL FISHES. 39 



to the body or head; the more elongated ones becoming real curved 

 spines, similar in general character to those of Acanthaspis, but differing 

 in tills, that they are not united by sutures with flat bones or plates, 

 but are the extremities of such plates drawn out into spines that must 

 have projected from the general surface. The broader plates are quite 

 thin and seem to have been applied to flat or arched surfaces, while 

 those which form spines have their remote extremities narrowed and 

 thickened till they become prominent and effective defensive organs. In 

 some instances the plates are triangular in outliije and seem to have been 

 thin cones of bone or enamel, supported by cartilaginous centres. As 

 the latter are decomposed, the sides, which were once widely separated, 

 are brought together, or crushed in like broken shells. 



The external surface of these plates is tuberculated in a vai-iety of ways. 

 In some instances the tubercles are large, scattered, smooth and round, 

 and resemble pustules. In other cases they are irregular and crowded ; 

 while occasionally they are in regular rows ; the interstices between them 

 being beautifully chased and ornamented. Along the margins of the 

 spinous extremities of tlie plates, the tubercles are elongated until they 

 become conical denticles. In a paper published by the writer some years 

 since in the "Bulletin of the National Institute" at Washington, descriptions 

 were given of a number of fish remains obtained at Delawai-e, Ohio, 

 by the late Dr. Mann. Among these, three species of " Oracanthus " 

 were described, viz. : 0. fragilis, 0. granulatus and 0. dbhreviatus ; all 

 of whicli I now believe to be simply phases of the varied scutes of 

 Aoantholepis. Some of the triangular ones seem to have resembled, in 

 form and function, the dermal spines of GUmaUus, Pa/rexus, etc., and it 

 is quite possible that they were set in greater or less number on the body. 

 In the reduced outlines, shown in Fig. 1 h, the relative positions of 

 two pairs of the larger scutes were given, and we may infer from these 

 that they were set along certain lines, more likely on the body than head 

 (since, except laterally, they show no signs of contact), just as the dermal 

 scutes are placed in Aocipenser. 



Much more material will be required before we can reconstruct Aoan- 

 tholepis, but its remarkable scutes are so frequently met with in the 

 Corniferous limestone, that it is evident it was numerously represented 

 in the Devonian sea. Future discoveries will, unquestionably, give us 

 the full information about it which we crave, but which is as yet beyond 

 our reach. 



On Plate LYI., Figs. 1, 1 a, represent a large pair of plates in their rel- 

 ative positions. A number of pairs of this kind liave been found, though 

 the individual plates are oftener met with entirely separated from their 

 connections. The extremity of Fig. 1 is not quite complete. Other speci- 



