956 CLASS PISCES. 



ossified ribs, large operculars, and Dipnoid teeth, but the form of 

 the fins and tail is unknown ; while the latter agrees with Phanero- 

 pleuron in the structure of the teeth and tail. 



Family Dipterid^:. — This family is characterised by the great 

 development of the cranial bones, the more or less ganoidal struc- 

 ture of the scales, the presence of jugular plates, the heterocercal 

 tail, the two distinct dorsal fins, and the greater size and breadth of 

 the scaled portion of the paired fins. Its range extends from the 

 Devonian to the Permian, and it shows signs of connecting the 

 preceding family with the Crossopterygian Ganoids. The teeth 

 (fig. 885) are of the same general type as those of Ceratodus, 

 but may carry a larger number of smaller ridges, which in some 

 instances (fig. 885, 1, 2) are ornamented with a number of cusps or 

 denticules. The typical genus Dipterus (fig. 884) comprises fishes 

 of small or medium size, with circular scales, and both the dorsal 

 fins placed in the hinder third of the body, the first being much 

 smaller than the second. The pectoral fins are long and paddle- 



Fig. 884. — Dipterus Valencicnnesi ; from the Devonian of Russia, two-thirds 

 natural size. (After Pander.) 



shaped ; while the pelvic pair, and the anal, are respectively placed 

 beneath the first and second dorsals. The quadrate is ossified ; 

 and there are also ossifications in the fin-rays and ribs. The teeth 

 (fig. 885, 1) carry numerous denticules on their ridges. This genus 

 is characteristic of the Devonian (Old Red Sandstone) of Europe. 

 Ctenodus attains considerably larger dimensions than the preceding 

 genera ; some of the species reaching a length of nearly five feet. 

 The teeth are characterised by their ridges carrying many cusps ; 

 and the scales are large and thin, with a rhomboidal contour, and 

 bearing traces of rows of denticules, with vascular grooves on the 

 inner side. The skeleton closely resembles that of Ceratodus, but 

 is more fully ossified ; and both this feature and the more numerous 

 cranial bones are regarded by Dr Fritsch as characters of greater 

 specialisation. The teeth (fig. 885, 2, 3) are frequently simpler 

 than those of Dipterus, and thus approximate to those of Ceratodus ; 

 while the form of the parasphenoid and palatopterygoid differs con- 

 siderably from that in the former. This genus ranges in Europe 

 from the Carboniferous to the Permian, being very abundant in the 



