THE BOW-FIN. 



5°9 



northern lakes, but remains of extinct species have been obtained, not only from 



the Eocene rocks of the same country, but likewise from the upper Eocene and 



Miocene strata of Europe. Carnivorous in its diet, preying both upon other fish 



and also upon aquatic crustaceans and insects, the bow-fin is capable of living for 



fully an hour out of water ; and when in its native haunts, especially where the 



water is foul, comes frequently to the surface to breathe, rising to the surface, and 



taking in large mouthfuls of air without the emission of a single bubble. When 



near the surface, this fish often utters a bell-like note, probabty due to the passage 



of air from the air-bladder. The breeding-season, during which the colours of the 



fish are more brilliant, lasts from May till the beginning of June. The bow-fins 



breed among floating islands of herbage fringing the great lakes. Here they lay 



thousands of minute eggs on the water-plants which form the base of a series of 



tunnels, composed partly of root-fibres, and partly of a moss-like growth. Of the 



nest thus formed, the male fish takes entire charge till the fry are hatched ; the 



development of the eggs being unusually rapid. The embryos, while agreeing in 



many respects with those of the typical ganoids, are stated to approximate in other 



points to those of the higher bony fishes. Megalurus, from the upper Jurassic, is 



an allied extinct genus with a short dorsal fin and fulcra ; while the Jurassic 



Eurycormus and Liodesmus likewise belong to the same family. 



Among several 



Extinct Families. . , „ ... „ 



extinct families or 



which the members are mostly 



of Jurassic age, we may notice 



the P achy cor midcv, as represented 



typically by Pachycormus, in 



which, while the body and jaws 



have the same form and structure 



as in the bow-fish, the notochord 



is persistent, and the ethmoid bone fused with the vomer to form a long beak ; the 



fin-rays being slender and closely set, the dorsal fin short, and fulcra absent or 



minute. Eugnathus and Caturus are well-known members of a third family 



distinguished by the vertebras being usually represented by incomplete rings, by the 



large fulcra, and the short dorsal fin ; the caudal 

 fin being forked. The Pycnodonts, ranging from 

 the Lias to the Eocene, constitute another family 

 group, in which the body is either deeply fusiform 

 or rhomboidal ; the notochord has no ossification 

 around it ; the cleft of the mouth is narrow ; the 

 teeth are small, nodular, and 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 Pycnodas; but we have 

 figured as an example of the dentition the lower 



RIGHT HALF OF THE LOWER JAW OF A "g« i <^ 1 «*° <*" tAaui^iv, w 



pycnodont (Mesodon).— After Gaudry. jaw of the allied Mesodon. Yet another family 



SKELETON OF AN EXTINCT AMIOLD (Cciturits). 



