THE BOW-FIN. 



59 



Extinct Families. 



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, probably 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 Liodesinus likewise belong to the same family. 



Among several 

 extinct families of 

 which the members are mostly 

 of Jurassic age, we may notice 

 the Pachycormidce, 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 vertebrae 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 Pycnodus ; but we have 



RIGHT HALF OF THE LOWER JAW OF A % ured as an example of the dentition the lower 

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



SKELETON OF AN EXTINCT AMIOID (Caturus). 



