TELEOSTOMI. 25 



Subclass TELEOSTOMI. (The True Fishes.) 



Skeleton usually bony, sometimes cartilaginous. Skull with 

 sutures ; membrane bones (opercle, preopercle, etc.) present ; gill 

 openings a single slit on each side ; gills with their outer edges 

 free, their bases attached to bony arches, normally four pairs of 

 these, the fifth pair being modified into tooth-bearing pharyngeals ; 

 median and paired fins developed, the latter with distinct rays. 

 Ova small ; no claspers. Heart developed, divided into an auricle, 

 ventricle, and arterial bulb. Lungs imperfectly developed, or modi- 

 fied to form a swim-bladder, or entirely absent. 



"We here include under one head the Ganoids and the Teleosts. 

 The former type is chiefly composed of extinct forms. "While 

 many of its representatives are extremely dissimilar to the bony 

 fishes, there is a gradual series of transitions, and between the 

 Halecomorphi of the Ganoids and the lsospondyli of the true 

 Teleosts, the resemblance is much greater than that between the 

 Halecomorphi and many other Ganoids The Ganoids are, in fact, 

 the most generalized of the true fishes, those nearest the stock from 

 which the Teleosts on the one hand, and the Dipnoi and Batrachia 

 on the other, have sprung. The real value or rank of some of 

 the current orders or suborders is still doubtful, (rtkeos, perfect ; 

 oro/jLa, mouth.) Omitting orders not represented in our waters, 

 we have the following analysis of 



Orders of True Fishes. 



a. Arterial bulb muscular, with numerous valves; optic nerves forming a 

 solid chiasma; ventrals abdominal; air-bladder with a duct; tail 

 strongly heterocercal throughout life; some fius usually with fulcra. 

 (Series Ganoidei.) 

 b. Skeleton cartilaginous : ventrals with an entire series of basilar seg- 

 ments. (Chcmdrostei.) 



c. Maxillary and interopercle obsolete; skin naked; air-bladder cellular. 



Selachostomi, VII. 

 cc. Maxillary and interopercle present; skin with bony shields; air- 

 bladder simple Glaniostomi, VIII. 



bb. Skeleton bony; ventrals with basilar segments rudimentary; air-bladder 

 cellular. (Holottei.) 



d. Vertebra opbthocoelian (concavo-convex) ; maxillary transversely 



divided in several pieces; scales rhombic, enamelled plates. 



GlNGLYMODI, IX. 



