Elasmobranchii. 



83 



The first table-case on the left and the adjoining wall-case are 

 filled with numerous spines and other dermal appendages of 

 cartilaginous fishes, perhaps mostly Elasmobranchs, which 

 cannot yet be precisely determined; they are conveniently 

 grouped together as Ichtliyodorulites (" fish-spine-stones "). [See 

 Fig. 111.] 



The earliest evidence of the sub-class is placed here, namely, 

 the dorsal fin-spines from the Ludlow Bone-bed (Upper Silurian) 

 and the Old Bed Sandstone, bearing the name of Onchus. 

 GtenacantTius is founded upon dorsal spines from the Carboni- 

 ferous. The huge Oracanthus pustulosus (Phoderacanthus), three 

 feet in length, from the Carboniferous Limestone of Bristol, is 

 the largest ichthyodorulite known ; and there are also triangular 

 paired spines of considerable size from the same formation, 



Wall-case, 

 No. 1. 



Table-case, 

 No. 25. 



FIG. 111. Spines of Elasmob ranch and Chimseroid Fishes. 



a, Acanthias (recent) ; 6, Callorhynchus (recent) ; c, Machceracanthus (Devonian) ; 

 d, Hylodus (Jurassic) ; e, Asteracanthus (Jurassic) ; /, Squaloraja (Lias) ; 

 g, Gyr acanthus (Carboniferous) ; li, Edestes (Carboniferous) ; i, Pleuracanthus 

 (Carboniferous). 



which are named Oracanthus Milleri, and provisionally associated 

 with several flat dermal plates having a corresponding orna- 

 mentation. Spines of Edestes (Fig. 11 Ih) occur in the Car- 

 boniferous of N. America, Australia, and Hussia, and are 

 remarkable for their curvature and the great size of the posterior 

 denticles ; the latter are in the form of serrated teeth, and led 

 their first discoverer, Prof. Leidy, to conclude that the fossils 

 were fragments of jaws. Gyracanthus (Fig. lllgr) occurs abun- 

 dantly in the British Carboniferous, and is represented both by 

 the well-known paired spines (with an ornament of angulated 

 ridges, and ordinarily abraded extremity), triangular dermal 



7 2 



