ICHTHYODORULITES. 



947 



present be determined, and several of which are probably referable 

 to the Chimeroidei. The earliest of these is Onchns (fig. 875, a), 

 from the Silurian bone-bed of Ludlow, to which genus may also 

 belong the dermal denticules (ibid., b) described under the name of 



Fig. 875. — Spine (a) oiOuchus teuta'striatus, and (b) Dermal plates of Tkclodus; 

 from the Silurian of Ludlow. 



Thelodus. In the Devonian of North America, and also in the 

 Upper Silurian or Devonian of Bohemia, large spines have been 

 described under the name of Machceracanthus (fig. 876), which 

 probably belonged to the dorsal fins. Gy?'acanthus is based on 



Fig. 876. —Fin-spine of MacJueracanthus major; from the Devonian of North America. 

 One-half natural size. (After Newberry.) 



unsymmetrical spines (fig. 852, 2), which, it has been suggested, 

 may belong to the pectoral fins. Other Carboniferous specimens 

 have been named Lophacanthus and Oracanthus (England), Eu- 

 acanthus (Russia), Xystracanthus (North America and India), and 

 Thaumatacanthus (India). 

 The spines described as 

 Oracanthus are now known 

 to belong to the head of 

 a Selachian, and not, as 

 at first supposed, to the 

 tail of a Placodermic Ga- 

 noid. It will be un- 

 necessary to mention a 

 number of other types 

 from various deposits ; but 

 we must not conclude 

 without referring to the 

 remarkable specimens (fig. 



877) from the Carboniferous of North America and Australia, to 

 which the name Edestus has been given. These have a highly 

 curved axis, bearing compressed lancet-like teeth, with serrated edges 



Fig. 877. - Part of (? caudal) spine of Edestus vorax ; 

 from the Carboniferous of North America. One-half 

 natural size. (After Newberry.) 



