CROSSOPTERYGII. 



175 



breathing air. The pituitary body retains its opening into the 

 buccal cavity through life.* The young Polypterus has an 

 external gill, which is attached to the operculum. 



Classification of Crossopterygii, living and extinct. 



Sub-order 1. OSTEOLEPIDA. 



Notochord more or less persistent. Pectoral fins rounded or pointed, 

 unibasal. Nares on the lower surface of snout. 



Fani. I. Tarrasiidae. Axonosts and baseosts of median fins in simple 

 regular series, much fewer in nmnber than the dermotrichia. Tarrasius 

 Traquau', Calciferous Sandstones (Lower Carboniferous) of Dumfriesshire. 



Fam. 2. Holoptychiidae. Body covered with overlapping cycloid 

 ganoid scales ; vertebral column vmossified ; pectoral fin with long pointed 

 scaled axis (mesorachic) ; tail hetero-diphycercal. Axonosts of each of 

 the dorsal and anal fins fused into a single piece with a broad distal 

 end, bearing three to six rod-like baseosts, which are much fewer than 

 and overlapped by the dermotrichia in all the iTiedian fins. Lateral jugular 



Fio. 103. — Holo/itychiuf flemw/)i, Devonian, Scotland, after restoration by Traqiiair, from 

 Woodward. 



plates, clavicles and infra-clavicles present ; the teeth have a compli- 

 cated folded structure. Holoptychius Ag. {Glyptolepis, Platygnathus Ag.) 

 Devonian ; isolated teeth have been described as Dendrodus, Lamnodus, 

 Apedodus. 



Fam. 3. Rhizodontidae. Like the preceding but with shorter pec- 

 toral and pelvic fins. Devonian, Carboniferous. Rhizodus. Strepsodus 

 Rhizodopsis, etc. 



Fam. 4. Osteolepidae. Ring vertebrae in the caudal region, Devonian. 

 Osteolepis, Thursius, Diplopterus, Megalichthys. 



Fam. 5. Onychodontidae, known only by fragments from the Devonian, 

 is placed here. 



Fam. 6. Coelacanthidae. Notochord persistent, vertebral cohunn un- 

 ossified. Axonosts of each of the dorsal and anal fins fused into a single 

 piece ; a series of axonosts, eqiial in number to the neural and haemal 

 spines present in the caudal fin above and below, each axonost directly 

 connected with a single dermal fin ray. Caudal fin diphycercal ; 

 air-bladder with ossified walls ; paired fins with short, obtuse axis ; only 

 one opercular bone. Lower Carboniferous to the Upper Chalk. Coela- 

 canthus Ag., Undina Miinst., Macropoma Ag., etc. 



* Bickford, Anat. Anz., 10, 1895. 



