FOSSILS AND PEDIGREES 



357 



sudden catastrophe, and their bodies rapidly interred by the 

 settUng of vast quantities of sediment. The Rhizodontidae 

 represent another aUied family, but the teeth are of a still 

 more specialised pattern and the scales of the cycloid type. 

 The genus Eusthenopteron (Fig. i 28b) also shows many Amphibian- 

 like characters, and has the curious double tail (see below). 



The second order, the Actinistia, includes a number of 

 specialised fishes derived from the Rhipidistia. The Coelacanthidae 

 are interesting forms, which, according to Sir Arthur Smith 



Fig. 128. PRIMITIVE CROSSOPTERYGIANS. 



A. Restoration of Holoptychius flemingi {Holoptychiidae) X \. (After Traquair) ; 



B. Restoration of Eusthenopteron fordi {Rhizodontidae), X \, (After Whiteaves.) 



Woodward, enjoy the distinction of having "perhaps the most 

 remarkable range of all known extinct fishes, occurring almost 

 unchanged throughout the whole series of formations from 

 the Lower Carboniferous to the Upper Chalk." The genus 

 Coelacanthus is found in the Carboniferous or Permian rocks of 

 England, Scotland, Europe, and North America, and other 

 important genera include Undina, a Jurassic fish (Fig. 129), 

 Diplurus from the Carboniferous of North America, and 

 Macropoma from the Cretaceous of England and Europe. The 

 double nature of the tail in Undina and Diplurus has been 

 described in detail in an earlier chapter (cf. p. 62). The scales 

 of the Coelacanths are cycloid, the paired fins rounded and 

 lobe-like, and an important feature of their internal anatomy 



