5°S 



GANOIDS. 



The Bow-Fin and its Allies, — Suborder Protospondyli. 



The so-called bow-fin {Amia calva) of the fresh waters of the United States 

 is the sole existing representative of a second and larger subordinal group, differ- 

 ing from the last by the imperfect ossification of the skeleton, the notochord beino- 

 either persistent throughout life, or if more or less completely replaced by vertebras, 

 those in front of the caudal region have their bodies composed of three distinct 

 elements (pleurocentra and intercentrum), which remain separate and alternating 

 even when fully developed. The lower jaw is complex, and composed of several 

 pieces ; in the pectoral arch the infraclavicular plate is absent; and the pectoral fin has 

 more than three basal elements belonging to the true internal skeleton ; while the 

 tail is always abbreviated heterocercal. 



3 





Existing Family. 



the bow-fin (i nat. size). 



Together with three extinct genera, the bow-fin constitutes a 

 family (Amiidce) characterised as follows. The lower jaw has its 

 suspending arrangement directed backwards, and the cleft of the mouth is wide ; 

 the degree of ossification of the vertebras is variable, although these often form 

 complete discs ; the body is elongate or fusiform ; the margins of the jaws are 

 armed with an outer series of large and conical teeth, internally to which are 

 smaller ones ; fulcra to the fins are either wanting or of minute size ; and the 

 dorsal fin is of variable, although usually of considerable length. Having the scales 

 thin, somewhat rounded, and overlapping, the bow-fin represents a genus in which 

 there are no fulcra, and the long dorsal fin occupies three-fourths the length of the 

 body, while the anal fin is short, the caudal rounded, and the throat furnished with 

 a single gular plate, followed by a number of branchiostegal rays. The single 

 existing species of the genus, which attains a length of 2 feet, is confined to the 

 fresh waters of the United States, where it is exceedingly abundant in some of the 



