THE VEUTEI3U/E IN FISHES. 47 



cartilaginous fishes of Cuvier, except the Sturgeons and Cliimer£e 

 (Stu?-io?iiens). It is as necessary, however, for the expression of 

 general anatomical propositions, to separate the Dermopto-i from the 

 Placoidei of Agassiz as from the Chondropteri/gil of Cuvier ; and 

 it is with this restriction that the Placoids will be referred to 

 in these Lectures, as answering namely to the Plagiostomes of 

 Cuvier. 



The Ganoid fishes are defended by plates or scales covered witli a 

 thick coat of enamel ; some of considerable dimensions and irregular 

 form, as in the Sturgeon ; more commonly angular and imbricated, as 

 in tlic Bony Pike (^Lepidosteus). Most of the species and genera of 

 this order have become extinct. The recent species included in it 

 by Agassiz differ materially in their anatomical characters. 



The Ctenoid fishes have scales formed of laminae of horn, or of un- 

 enamelled bone, with the posterior margin pectinated, like a comb ; 

 e. g., the Perch, and most of the Acantliopterygii of Cuvier. 



The Cycloid fishes have their scales composed of lamina3 of horn 

 or unenamelled bone, of a rounded form, with smooth and simple 

 margins. The Carp, the Salmon, the Herring,, and many other Ma- 

 lacopterygii of Cuvier, are examples of this order. 



Linnceus divided the bony fishes into the orders Jugulares, Tho- 

 racici, Abdominales, and Apodes, according to the position or the 

 absence of the ventral fins. Cuvier divided the bony fishes, ac- 

 cording to the structure of the fins, into Acanthopterygii and 

 Malacopterygii. Not many general anatomical proj^ositions, how- 

 ever, can be expressed with regard to these orders. A more natu- 

 ral arrangement has been founded upon a consideration of both 

 external and internal anatomical characters by Prof. J. Miiller 

 (xxv.), which, with some modifications, I here adopt ; arranging the 

 class of Fishes, as follows, in the ascending series : — 



Classis PISCES. 



Ordo I. Dermopteri. 



Endo-skeleton unossified ; exo-skeleton and vertical fins muco- 

 dermoid ; vermiform, or abrachial and apodal ; no pancreas ; no air- 

 bladder. 



Suborder I. Pharyngobhanchii, seu Cirrhostomi. 



Gills free, pharyngeal, inopei"culate ; no heart. 



Fam. Amphioxidce. Example *, Lancelet. 



* Tlicse are cited under tlieir common linglish names, wlierc sncli exists. 



