486 FISHES CHAP. 
arborescent appearance in transverse sections. Vertebral column 
acentrous. Genera :—Holoptychius' (Fig. 277), Old Red Sand- 
stone of Scotland; Devonian of Belgium, Russia, North America, 
and East Greenland. Gilyptolepis has a similar range. 
Fam. 4. Coelacanthidae.°—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. Radialia 
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 
Ma 
Fic. 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 +. 
(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) ’* 
' Traquair, Proc. Roy. Soc. Edinb. xvii. p. 388. 
* Reiss, Die Coelacanthinen, Palaeontogr. xxxi. 1888, p. 1; Smith Woodward, 
Brit. Mus. Cat. Foss. Fishes, ii. 1891, p. 394. 
® See also Kurtus indicus, p. 688. 
