98 Bulletin 47, United States National Museum. 



We here include under one head the GANOIDS and the TELKOSTS. The 

 former group is chiefly composed of extinct forms. While many of its rep- 

 resentatives are extremely dissimilar to the bony fishes, there is a gradual 

 series of transitions, and between the CYCLOGANOIDEA of the GANOIDS and 

 the CLUPEOIDS and others of the true TELEOSTS, the resemblance is much 

 greater than that between the CYCLOGANOIDEA 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. (rtAffof, 

 perfect; ar6fj,a, mouth.) 



Omitting orders not represented in our waters, we have the following 

 analysis of 



ORDERS OP TRUE FISHES. 



a. Arterial bulb muscular with numerous valves; optic nerves forming a solid chiasma; ven- 

 trals abdominal; air bladder with a well developed duct; tail strongly heterocercal 

 throughout life; some fins usually with fulcra. (Series Ganoidei.) 

 CHONDROGANOIDEA : 

 b. Skeleton cartilaginous; ventrals with an entire series of basilar segments. 



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



SELACHOSTOMI, I. 

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



CHONDBOSTEI, J. 

 HOLOSTEI OR HYOGANOIDEA: 

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



d. Vertebrae opisthocoelian (concavo-convex); maxillary transversely divided into sev- 



eral pieces; scales rhombic, enameled plates. RHOMBOGANOIDEA, K. 



del. Vertebrae amphicosliau (double concave); maxillary not transversely divided; scales 



cycloid. CYCLOGANOIDEA, L. 



aa. Arterial bulb thin, with a pair of opposite valves; optic nerves crossing, not forming a 



solid chiasma. (Series Teleostei.) 



e. Anterior vertebra (about 4), much modified, cob'ssified and provided with ossictila aud- 

 itus, or weberian apparatus; shoulder girdle suspended from the skull by a bony 

 post-temporal; mesocoracoid arch well developed. Air bladder (if present) connected 

 by a slender air duct with the intestinal canal, this persistent throughout life; 

 ventral fins (if present) abdominal, without spines, their basilar segments rudi- 

 mental. (OSTARIOPHYSI.) 



/. Maxillary bone imperfect, forming the base of a conspicuous barbel; no suboper- 

 cle nor symplectic bone; no scales; supraoccipital and parietals coossified. 



NEMATOGNATHI, M. 



ff. Maxillary bone perfect (rarely wanting) and never entering into the base of a 

 barbel; subopercle and symplectic present; scales usually present. 



PLECTOSPONDYLI, N. 

 ee. Anterior vertebrae unmodified, similar to the others, or more elongate ; separate and 



without ossicula auditus. (Descendants of Holostean Ganoids.) 

 g. Body eel-shaped, provided with very many (100 to 250) vertebrae; scales minute or 



wanting; no ventral fins; gill openings restricted. 

 h. Gill arches 4 pairs; the hindmost being modified as pharyngeal bones; pal- 



atopterygoid arch present. 



i. Premaxillary, maxillary, and palatine bones well developed and distinct 

 from each other as in ordinary fishes; no paired fins; gill openings 

 confluent; shoulder girdle. joined to the cranium in our species (but 

 not in all). SYMBRANCHIA, 0. 



