6 



Fossil Fishes. 



Table-case, 

 No. 25. 



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

 filled with numerous spines and other dermal appendages of cartila- 

 ginous fishes, perhaps mostly Plagiostomes, which cannot yet be 

 precisely determined ; they are conveniently grouped together as 

 Ichthj/odorulites ("fish-spine-stones ") [See Figs. 1 1 — J 3, pp. 5 & 6]. 



The earliest evidence of the order 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. Ctenacan- 

 thus is founded upon dorsal spines 

 from the Carboniferous, and a 

 complete fish, with the spines in 

 position in front of the dorsal fins, 

 is exhibited from Eskdale, Dum- 

 fries. Possibly some of the teeth 

 named Cladoclus pertain to the 

 same form. The huge Phodera- 

 canthus, three feet in length, from 

 the Carboniferous Limestone of 

 Bristol, is the largest ichthyo- 

 dorulite known ; and 

 also triangular paired 

 considerable size from the same 

 formation, which are named Ora- 

 canihus and provisionally associated 

 with several flat dermal plates 

 having a corresponding ornamenta- North America, 

 tion. Spines of Edestes (Figs. 11 h, 12) occur in the Carboniferous 

 of N. America, Australia, and Russia, 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. 13) occurs abundantly in the British Carbon- 



there are 

 spines of 



Fig. 12.— Portion of spine of Edestes 

 vorax, Coal-meafiures, Indiana, U. S. 



Fig. 13. — Spine of Gyracanthus formosvs, showing abrasion of the apex, Coal- 

 measures, Scotland. 



iferous, and is represented both by the well-known paired spines 

 (with an ornament of angulated ridges, and ordinarily abraded 

 extremity), triangular dermal bones, and shagreen granules : the 

 teeth probably bear another name. Acondylacanthus resembles the 

 spine of a Ray : and Erismacanthus and Lispacanthns are very 

 suggestive of the rostral spine of male Chimseroids. 



The Jurassic Aster acanthus (Fig. 11<?) and Pristacanthus are 

 evidently dorsal fin-spines, and the former may be correlated in 

 part with the teeth known as Strophodus. 



