CLASSIFICATION OF VERTEBRATA 



Chlamydoselache anguineus, approaching the Proselachii. 



Japan, Azores, Norway. 

 Heptanchus, Hexanchus, Pristis, Scyllium, Mustelus, 



Galeus, Squatina, Zygaena, Cestracion, etc. 

 2. Sub-order RAIAE. Pectoral fins fused with and 

 surrounding the sides of the head. 



Beginning clearly in the Jurassic strata. 

 Eaia, Trygon, Myliobates, Torpedo, etc. 



II. Division ACANTHODI, Agassiz. With five Elasmo- 

 branch gill-clefts, but each with an external fringe-flap. Mouth 

 sub-terminal. 



Vertebrae acentrous. Without mixipterygia. 

 Paired and median fins with a strong dermal spine. 

 Large dermal bones on the jaws ; dermal armature of trunk 

 and cranium consisting of small granules. 



Acanthodes. From Devonian to Permian, Europe. 

 Upper Devonian : pelvic fins almost as large as the 

 pectorals, and placed midway between pectorals and anal fin. 

 Lower Carboniferous : pel vies reduced in size. 

 Upper Carboniferous : pelvics much reduced, and placed 

 far forwards towards the enlarged pectorals. 



Lower Permian : pelvics insignificant ; pectorals enormous, 

 and closely approximated towards each other. 



Chiracanthus. Old Red, Scotland ; both fins well de- 

 veloped. 



Diplacanthus. Old Pied, Scotland; with clavicle and 

 cleithrum. 



III. Division HOLOCEPHALI, Mueller. Palato-quad- 

 rate bar fused with the cranium. 



Vertebrae acentrous ; numerous calcified rings in the 

 notochordal sheath. 



Agreeing with Elasmobranchi : males with mixipterygia ; 

 absence of membrane bones ; conus arteriosus with three series 

 of valves. 



Agreeing with Tectobranchi : four gill-clefts, with one large 

 operculum ; the gill-septa are thin and incomplete, no longer 

 reaching the surface ; with a few large teeth resembling those 

 of Dipnoi ; mouth subterminal. 

 Ptyctodus. Devonian. 



