100 Bulletin 47, United States National Museum. 



Series GANOIDEI. 



(THE GANOID FISHES.) 



The name GANOIDEI was first used by Agassiz, for those fishes which are 

 armed with bony plates, instead of regular cycloid or ctenoid scales. 

 Later, Johannes Miiller restricted the group to those fishes thought to 

 show more or less distinct reptilian or batrachian affinities, and especially, 

 affinities with the mailed fishes of the Devonian and Carboniferous ages. 

 The group is a heterogeneous one, and one practically scarcely susceptible 

 of definition. In some of the GANOIDS, the air bladder still retains its 

 original function, a lung. The existence of the solid optic chiasma, tbe 

 presence of several valves in the arterial bulb, and of a more or less devel- 

 oped spiral valve in the rectum, distinguish the living GANOIDS from all 

 TELEOSTS, but none of these characters can be verified in the extinct 

 forms. We begin the series with forms having the skeleton still cartila- 

 ginous as in the sharks, but even less developed, (ydvoc, splendor, from 

 the enameled scales.) 



CHONDROGAIVOIDEA. 



(THE CARTILAGINOUS GANOIDS.) 



Skeleton chiefly cartilaginous, the vertebral column entirely so, the 

 vertebral segments little developed, arranged along the notochord. Ante- 

 rior vertebrae simple, imperfectly formed. Ventral fins abdominal, with 

 an entire series of basilar segments. No suboperculum or preoperculum. 

 Branchiostegal single or wanting ; a mesocoracoid arch ; no symplectic 

 bone. Mesopterygium distinct; interclavicles present.* Arterial bulb 

 with several pairs of valves. Optic nerves forming a chiasma. Intestine 

 with a spiral valve. Air bladder connected by a duct with the resophagus. 

 Tail heterocercal, its fin with fulcra. Skin naked or armed with bony 

 plates, never with true scales. This group comprises two orders. Its 

 place seems to be intermediate between the Sharks and the Catfishes, 

 though without close relation to either. (CHONDROSTEI, Giinther, Cat., 

 vin, 332-347.) (x'ovdpos, cartilage ; Ganoidea.) 



ANALYSIS OF ORDERS OF CHONDROGANOIDEA. 



a. Maxillary and interoperclo obsolete; skin naked; brauchihyals cartilaginous; air bladder 

 cellular. SELACHOSTOMI,-!. 



ao. Maxillary and interopercle present; skin with bony shields; branchihyals osseous; air 

 bladder simple. CHONDUOSTEI, J. 



Order I. SELACHOSTOMI. 

 (THE PADDLE-FISHES.) 



Notochord persistent, the division into vertebrae imperfect. Mesocora- 

 coid developed; no symplectic bone; premaxillary forming border of 

 mouth; no suboperculum, preoperculum, nor interoperculum ; mesopte- 



* The osteological characters here and in some other parts of this work are partly taken from 

 Cope's "Contribution to the Ichthyology of the Lesser Antilles," Trans. Am. Phil. Soc., 1870. 



