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, 

 vinibasal. Nares on tlie lower surface of snout. 



Fam. 1 . Tarrasiidae. Axonosts and baseosts of median fins in simple 

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

 Traquair, Calciferous Sandstones (Lower Carboniferous) of Dumfriesshire. 



Fam. 2. Holoptychiidae. Body covered with overlapping cycloid 

 ganoid scales ; vertebral column unossified ; 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-Hke baseosts, which are much fewer than 

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



Flo. 103.— Iloloflty<:.hiuK fiemingi, Devonian, Scotland, after restoratiuu by I'raquair, from 

 Woodward. 



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

 cated folded structure. Holoptychitis Ag. (Glypfolepis, Platygnathus Ag.) 

 Devonian ; 'solated teeth have been described as Dendrodtis, Lamnodus, 

 Apedodus. 



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

 toral and pelvic fuis. Devonian, Carboniferous. Rhizodua, Strepsodus 

 Rhizodopsis, etc. 



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

 Osteolepis, Thursius, Diploptertis, Megalichthys. 



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

 is placed here. 



Fam. 6. Coelacanthidae. Notochord persistent, vertebral column im- 

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

 piece ; a series of axonosts, equal hi 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 ; onl^- 

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

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



* Bickford, Anat. Am., 10, 1895. 



