ROOM v. CELACAJTTHS. 433 



striated, hollow teeth, very closely resembling those of sau- 

 rians ; the head is encased in thick osseous plates, as in the 

 recent Polypterus; the body is covered by large granulated 

 scales. There are a fine lower jaw, teeth, and scales of 

 M. Hibberti in this Case. 



Rhizodus. This fish, though clearly distinct from the Me- 

 galichthys, is often confounded with it by collectors. The 

 genus was established from some detached teeth and jaws; l 

 the scales are thinner, larger, and smoother than in Mega- 

 lichthys, and their enamelled surface is finely punctated. 

 The great strength of the cephalic plates, and of the jaws and 

 teeth, of this powerful carnivorous fish, are well shown in the 

 fossil remains from Burdie House, and Carluke, in Perthshire, 

 which lie on the middle shelf of this compartment of 

 Case B. 



The conditions under which the remains of these enormous 

 fishes are found imbedded at Burdie House, are highly interest- 

 ing, for the limestone and marls in which they occur are at 

 the bottom of the Coal formation, and abound in the foliage 

 of ferns and other terrestrial plants, freshwater shells and 

 crustaceans, and coprolites. These deposits must, therefore, 

 have been formed in a lake, or estuary, frequented by pre- 

 daceous sauroids ; in like manner, as we have already shown, 

 the bays and streams of the Country of the Iguanodon 

 swarmed with the lepidoid fishes of the Wealden epoch. 



Before proceeding to the next family of Ganoids, I would 

 direct the palaeontologist to the specimens of Eugnathus 

 J(E. sjyeciosus), Wall-case B (9), and Ptycholepis (P. Bollensis), 

 from the Lias of Wirtemberg ; two genera of voracious sau- 

 roids, which are characterised by their unequal-lobed tail, 

 large fins, and furrowed scales. Eleven species of Eugnathus 

 have been discovered in the Has at Lyme Regis; only one 

 species of Ptycholepis is known. 



CELACANTHS (hollow spine). This family of Ganoids is dis- 

 tinguished from the rest of the order by the tubular or hollow 

 structure of the fin-rays and spinous processes ; 2 the prolonga- 



1 See Dr. Buckland's " Bridgewater Essay," PI. XXVII. 



* Mr. Miller observes, " they were cartilaginous within, and covered 

 externally by a thin osseous crust or shell, which alone survives." 

 " The Asterolepis," p. 37. 



F F 



