PISCES. 205 



Order VII. Lophobranchii, 



Internal skeleton only partly ossified. Scales ganoid. Gills tufted, gill- 

 opening small. Swimming bladder without air-duct. 



HippocampidaB. Syngnathidae. 



Order VIII. Ganoidei. 



Internal skeleton bony or cartilaginous. Scales ganoid. First fin-ray 

 usually a spine. Swimming bladder with an air-duct. 



Sauridae. Sturionidae. Cephalaspidae. 



PycnodontidaB. Acanthodei. 



Lepidoidei. Dipteridae. 



Order IX. Protopteri. 



Internal skeleton partly bony, partly cartilaginous. Scales cycloid. 

 Pectorals and ventrals as flexible filaments. Gills filamentary, free. No 

 pancreas. Swimming bladder as a double lung, with an air-duct. Intestine 

 with a spinal valve. 



Sirenoidei. 



Order X. Holocephali. 



Internal skeleton cartilaginous. External skeleton as placoid grains. 

 Most of the fins with a spinous first ray ; ventrals behind the pectorals. 

 Gills laminated, attached by their margins ; a single external aperture. 

 No swimming bladder. Intestine with a spiral valve. Copulation between 

 the sexes. 



Chimseroidei. Edaphontidae. 



Order XI. Plagiostomi. 



Internal skeleton cartilaginous, or partly ossified. External skeleton 

 placoid. Gills fixed ; with five or more gill-openings. Swimming bladder 

 none. Scapular arch not attached to head. Ventrals behind the pec- 

 torals. Intestine with spiral valve. 



HybodontidaB. Lamnidae. Rhinobatidae. 



Cestraciontidas. Alopeciidae. Torpedinidae. 



Notodanidae. Scymniidae. Raiidae. 



Spinacidae. Squatinas. Trygonidae. 



Scylliidae. Zygaenidae. Myliobatidas. 



Nictitantes. Pristidoe. Cephalopteridae. 



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