FOSSIL FISHES. 37 



since tliey aie marked with pectinated ribs much in tlie same way, bnt 

 their attachment to bony plates and the denticiihition of hoth sides of the 

 pointed extremity shows distinctly that they have only a superficial resem- 

 blance to the defensive spines of Elasmobranch fishes. AVhen complete 

 and seen in position they i-eveal their afiinities witli the lateral cornua of 

 the cephalic buckler of Cephalaspis. The external surface of tlie plates 

 to which these spines are attached is marked with a conspicuous and 

 peculiar ornamentation, mucii like that of Bothnolepin^ a series of con- 

 voluted, locally parallel, raised and beaded lines. As the cranial plates of 

 Acanthasjyis have never been found in connection, it is impossible to give 

 at present the form of the cranium, but they are seen to be in pairs, and 

 it is highly probal)le that when united they formed a rounded head-buck- 

 ler which differed fi-om that of Ceplialaspis mainly in being composed of 

 a series of separable plates, instead of forming a solid box. 



ACANTHASPIS ARMATUS (n. Sp.). 

 Plate LV., Figs. 1-6. 



Cranium consisting of a number of bony plates, forming several pairs, 

 and ditfering considerably in outline. To at least one of these pairs are 

 attached, on the outer margin, strong, slightly curved, carinated, tubercu- 

 lated and toothed spines. The external surface of the plates is covered 

 with convoluted or radiated raised lines, which are more oi" less tubercu- 

 lated. 



Sevei'al cranial plates of this species are represented in the figures now 

 published, and tliese will give a better idea of their form and marking 

 than any verbal description can do. These plates, and the spines wliich 

 are connected with some of them, are frecpiently met with in the Cornif- 

 erous limestone of Sandusky and Delaware, but, like the cranial plates of 

 Onychodus, they seem to have had no bony attachment to each other, 

 and, in the dissolution of the body of the fish which bore them, they have 

 been widely separated. There is little doubt that, sooner or later, some 

 cranium will be found in which the bones hold their normal positions, 

 and, from such a specimen, a more complete description of tlie fish can be 

 drawn than can now be given. Waiting the discovery of such complete 

 material, tbe plates now figured will, doubtless, be looked upon with inter- 

 est, and will stimulate the search for more remains of what has hitherto 

 been an entirely unknown Devonian fish. 



Figures 1 and 2 of Plate LY. represent a pair of plates wliich occupied 

 corresponding positions on opposite sides of the head (?) of, perhaps, the 



