PISCES. 13 



bb. Gill opening single, leading to four gill clefts ; jaws coalescent with the 

 skull; a rudimentary opercle ; teeth coalescent forming bony plates. 



( Chimairas.) HOLOCEPHALI, page 24. 



aa. Gills free, attached at base only to the gill arches; gill opening single on 

 each side ; eggs comparatively small and numerous ; no claspers ; mem- 

 brane bones present on head; cerebral hemispheres not united. ( True 

 Fishes.) . TELEOSTOMI, page 25. 



