488 GEOLOGY. 



sented by Holoptychius, Eusthenerpteron, and their allies. These show 

 many resemblances to the amphibians in their teeth and skull-bones, 



Fig. 220. — Dipterus valenciennesi, restoration by Traquair; from the Old Red Sand- 

 stone, North Scotland; about one-fifth natural size. 



and these structural resemblances of the hard parts count for more 

 than the physiological resemblances between the lung-fishes and the 

 amphibians. In the Holoptychius (Fig. 221) the enamel of the teeth 



Fig. 221. — Restoration of Holoptychius flemingi by Traquair; about one-eighth 

 natural size; from Old Red Sandstone, Dura Den, Scotland. (After Wood- 

 ward.) 



vas intricately infolded, giving a dendritic structure in cross-section, 

 as illustrated in Fig. 222, which much resembles the labyrinthodont 



Fig. 222. — Cross-section of tooth of Holoptychius, much magnified. (From Smith- 

 Woodward, after Pander.) 



structure of certain of the early amphibians. The holoptychians 

 appear to have been rather rare in the early Devonian, but to have 



