2886 



THE BONY FISHES AND GANOIDS 



aggregated into a pavement, without vertical successors; the gill cover is of a 

 very simple type; branchiostegal rays and fulcra are alike absent; and the dorsal 



fin is elongated. The family is typically repre- 

 sented by the genus Pycnodus; but we have 

 figured as an example of the dentition the lower 

 jaw of the allied Mesodon. Yet another family 

 {Dapedudee) is represented by Dapedius, Lepi- 

 dotus, and several other allied genera, in which 

 the body is more or less deeply fusiform, the 

 suspensory apparatus of the lower jaw either ver- 

 tical or inclined forward, the cleft of the mouth 

 narrow, the teeth cyclindrical or in the form of 

 button-like knobs, the vertebrae not more- than 

 rings, and the dorsal fin not extending more than 

 half the length of the body. In this family the 

 teeth have vertical successors ; and while some 

 of the earlier genera date from the Trias, the 

 scale tooth {Lepidotus), of which an example is figured in the illustration, 

 survived till the Chalk. Some of the species of this genus attained very large 



RIGHT HALF OF THE LOWER JAW OF 

 A PYCNODONT (Mesodon). 



(After Gaudry.) 



ceo 



THE GIANT SCALE TOOTH WITH A DETACHED SCALE AND TEETH. 

 (Much reduced.) 



dimensions; and their remains are beautifully preserved in the Lithographic 

 Limestone of Bavaria. In all these the scales are of the typical quadrangular 

 ganoid type. 



THE STURGEON TRIBE SUBORDER Chondrostei 



This important suborder brings us to the last group of the fan-finned fishes 

 (Actinopterygii), which forms a division by itself differing in several important 

 particulars from the one including the whole of the foregoing suborders; the more 

 important characteristics of the first division having been given on p. 2701. Whereas 

 in that division the number of dermal rays in the dorsal and anal fins is equal to 

 the supporting elements in the true internal skeleton, in the present division the 

 dermal rays are more numerous than their supports. Then, again, whereas in the 



