PISCES. 203 



Plagloslomes of authors fall under this order. The families are : Rajacei, 

 Ceslraciones, Hyhodontes, Squalini, ClihncercB, Ichthyodorulitkcs. 



II. Ganoids. Here the scales are bony and covered externally with 

 enamel, generally angular and continuous. Most Ganoids are extinct ; 

 the most striking and typical recent representation is the Lepidosteus or 

 gar-fish. Families: Sturionini, Lopholrranchii, Gymnodontes, Sclerodermi, 

 Cephalaspides, Pycnodontes, C(£lacanthi, Sauruidei, Lepidosteini. 



III. Ctenoids. This order corresponds nearly to the Acanthopterygii 

 of Cuvier. It is characterized by the roughness of the scales, the border 

 of which is generally dentated, and by the usual presence of spinous rays 

 in the dorsal and anal fins. Families : Mugiloidei, Aulostomi, Pleuro- 

 nectidei, Squamijyennes, Theutye$, Gohioidei, ScicBiioidei, Sparoidei, Per- 

 coidei. 



IV. Cycloids. These are represented by the greater number of the 

 Malacopterygii of Cuvier. The scales are generally smooth, and not 

 dentated. The dorsal and anal fins have generally soft rays. Fami- 

 lies : Anguilliformes, Halecoidei, Esocini, Cyprinodontes, Cyprini, Lab- 

 roidei, Lophioidei, Blennioidei, Sphyrcsnoidei, Xiphioidei, Scomberoidei. 



The most recent classification of fishes is that of Prof. J. Miiller (Ueber 

 den Bau und die Grenzen der Ganoiden u. iiber das natiirliche System 

 der Fische. 1846). We append a brief summary of this system as modi- 

 fied by several authors. 



Order I. DgRMOPTERi. 



Internal skeleton unossified : external skeleton and vertical fins mucous, 

 naked. Shape vermiform, or without any lateral fins. No pancreas nor 

 air-bladder. 



Sub-order 1. Pharyngobranchii. 

 Amphioxidae. 



Sub-order 2. Marsipobranchii. 

 Myxinoidei. Petromyzontidee. 



Order II. Malacopteri. 

 Internal skeleton ossified. Scales of the external skeleton mostly cycloid, 

 in some ganoid. Fins all supported by rays, all of these jointed excepting 

 sometimes the first in the dorsal and pectoral ; abdominal or apodal. Gills 

 free, operculate. A swimming bladder and air duct. 



Sub-order 1. Apodes. 

 Symbranchidae. Muraenidae. Gymnotidee. 



Sub-order 2. Abdominales. 

 Clupeidse. Galaxidae. Cyprinodontidae. 



Salmonidre. Esocidae. Cyprinidae. 



Scopelidae. Mormyridae. Siluridae. 



Characini. Hypsocidae. 



407 



