OF THE ASTEROLEPIS. 33 



casionally from five to six inches in diameter. Even in the 

 Holoptychius NohilissimuSj in an individual scarcely exceeding 

 two and a half feet in length, they measured from an inch and 

 a half to an inch and three quarters each way. In the splen- 

 did specimen of this last species in the British Museum, there 

 occur but fourteen scales between the ventrals, though these 

 lie low on the creature's body, and the head ; and in a spe- 

 cimen of a smaller species, — the Holoptychius Andersoni, — 

 but about seventeen. The exposed portion of the scale was 

 in most species of the family curiously fretted by intermingled 

 ridges and furrows, pits and tubercles, which were either 

 boldly relieved, as in the Holoptychius^ or existed, as in the 

 Glyptolepis, as slim, delicately chiselled threads, lines, and 

 dots. The head was covered by strong plates, which were 

 roughened with tubercles either confluent or detached, or 

 hollowed, as in the Bothriolepis, into shallow pits. The jaws 

 were thickly- set with an outer range of true fish-teeth, and 

 more thinly with an inner range of what seem reptile-teeth, 

 that stood up, tall and bulky, behind the others, like officers 

 on horseback seen over the heads of their foot-soldiers in 

 front. The double fins, — pectorals and ventrals, — were cha- 

 racterized each by a thick scale-covered centre, fringed by the 

 rays ; and they must have borne externally somewhat the 

 form of the sweeping paddles of the Ichthyosaurian genus, — 

 a peculiarity shared also by the double fins of the Dipterus. 

 The single fins, in all the members of the family of which 

 specimens have been found sufficiently entire to indicate the 

 fact, were four in number, — an anal, a caudal, and two dorsal 

 fins ; and, with the exception of the anterior dorsal, which 

 was comparatively small, and bent downwards along the back, 

 as if its rays had been distorted when young,* they were all 

 of large size. They crowded thickly on the posterior portion, 



* A peculiarity which also occurs in the anterior dorsal of the D-lp- 

 terus. 



