480 FISHES CHAP. 



arborescent appearance in transverse sections. Vertebral column 

 acentrous. Genera: Holoptychius 1 (Fig. 27V), Old Eed Sand- 

 stone of Scotland ; Devonian of Belgium, Eussia, North America, 

 and East Greenland. Glyptolepis has a similar range. 



Fam. 4. Coelacanthidae. 2 Scales cycloid. Paired fins ob- 

 tusely lobate. Tail symmetrical but apparently gephyrocercal, 

 usually with a protruding axial vestige of the disappearing 

 terminal part of the tail and of the proper caudal fin. Eadialia 

 of the functional caudal lobes agree in number with the con- 

 tiguous neural and haemal arches and dermal fin-rays, the 

 diagnostic feature of Smith Woodward's Actinistia. Proximal 



FIG. 278. Restoration of Undina gulo. Lower Lias of Dorset. Scales and supra- 

 clavicle omitted. The ossified air-bladder is shown beneath the anterior part of 

 the vertebral column. The facial bones in front of the orbit are unknown, and 

 the cheek-plates are supposed to be arranged as in other Coelacanths. x about f. 

 (From Smith Woodward.) 



radials of the dorsal and anal fins fused into a single, internally- 

 forked basipterygium in each fin. Teeth simple. Vertebral 

 column acentrous. The skull presents several interesting 

 features. The hyomandibular and the palato-quadrate bar, 

 for example, are fused on each side into a continuous tri- 

 angular bone, articulating with the cranium above and with 

 the lower jaw below. The opercular skeleton is reduced to an 

 operculum and two jugular plates. A very singular feature in 

 these Fishes is the ossification of the walls of the air-bladder 

 (Fig. 278), a structural modification which has no parallel in 

 Fishes, except in certain Teleosts (Siluridae and Cyprinidae) 3 



1 Traquair, Proc. Roy. Soc. Edirib. xvii. p. 388. 



2 Reiss, Die Coelacanthinen, Palaeontogr. xxxi. 1888, p. 1 ; Smith Woodward, 

 Brit. Mus. Cat. Foss. Fishes, ii. 1891, p. 394. 



3 See also Kurtus indicw, p. 688. 



