154 



PALEONTOLOGY. 



single dorsal situated in front of the anal ; Acanlhodes, in 

 which the dorsal is situated behind the anal ; and Dipla- 

 canthus (fig. 64), in which there are two dorsals. 



The Diplacanthus striatus is found in the "old red" of 

 Cromarty. In fig. 64, as in the other figures, p is the pectoral 



Fig. 64. 

 Diplacanthus striatus. 



fin, d the dorsal, v the ventral, a the anal, and c the caudal. 

 In this species the upper lobe of the caudal is much pro- 

 longed. The fin-spines in the Acanthodii were, like those 

 of the recent dog-fish (Sjpinax), simply imbedded in the 

 flesh, with their base, as it were, unfinished ; not provided, 

 as in the Siluroids and other modern bony fishes, with a 

 joint-structure. 



Cheirolepis, with the minute scales of the family, has the 

 dorsal behind the anal, but has no spine in any fin: the 

 mouth is large, the teeth small and uniserial. Some species 

 of the present family, Acanthodes Bronnii, Ac. sulcatus, existed 

 in the seas of the carboniferous period. 



Family III. — Coelaoanthi. 



The species of this family are characterized by the hollo w- 

 ness of the rays or spines ; whence the name. The caudal fin 

 has a peculiar structure, the vertebral column being continued 



