BOW-FINS. 81 



or Teleostei than do any of the other fishes of the order Asty- 

 lopterygii. The body is somewhat compressed laterally, and 

 covered with thin, flexible, cycloid scales ; the dorsal fin is more 

 or less long and low, the anal fin is short-based ; the fin-rays are 

 robust ; there are no fulcra, except in Megalurus. The tail is 

 nearly homocercal, with a rounded hinder margin ; it is distinctly 

 heterocercal in the young. The vertebrae are well ossified (except 

 in Lioclesmus) and are amphicoelous [i. e. the centra are hollow 

 both in front and behind) ; in the caudal region the half-centra 

 remain distinct. The skull bears a close resemblance to that 

 of the Teleostei, but the vomer is paired, and there is no supra- 

 occipital bone. The opercular apparatus is complete, and there 

 is a large median jugular plate. The premaxillary bones meet, 

 and are not separated as they are in the next family. 



The Bow-fin, Amia calva, 227, of the North American lakes Bow-fin. 

 and rivers, is the sole existing member of the family; it grows 

 to about 30 inches in length ; it is voracious and feeds upon 

 crustaceans and insects. The general coloration is a dark mottled 

 green ; the male is smaller than the female and is distinguished 

 by the presence of a round black spot encircled by a margin of 

 orange at the base of the tail. The Bow-fin is valueless as food, 

 the flesh being soft, watery and ill-flavoured. The air-bladder 

 is cellular and lung-like, and opens into the dorsal wall of the 

 pharynx. Owing to the high development of the air-bladder as 

 a lung- sac the fish can live out of water for a long time. 



The Pachycormidte (e. g. Hypsocormus, 229) are an extinct Pachy- 

 family of large-mouthed, predatory fishes related to the Amiidse. corm idae. 

 The scales are thin and rhombic, sometimes rounded at the 

 postero-inferior angle. The dorsal fin is short based, with 

 fin-rays slender and closely set, and fulcra few or absent. The 

 ethmoid region of the cranium is fused with the vomerine bones, 

 and is more or less produced in front of the mouth, forming 

 a prominent rostrum which separates the two premaxillge. The 

 branchiostegal rays are numerous ; there is a single, large 

 jugular plate. Some of the teeth are large and conical. Feeble 

 ossifications sometimes occur in the sheath of the notochord, 

 but in most cases the notochord persisted without reduction in 



