80 



PISCES. 



directly apposed to the blunt distal extremities of the neural and haemal 

 spines of the axial skeleton. A single stout dermal ray is connected with 

 each of these elements by a simple overlapping articulation ; and a vacant 

 space is left in the fossils apparently for the production of the extremity 

 of the axial skeleton beyond this fin. None of the fm-rays are bifurcated, 

 but all are more or less articulated distally, and there is a double series of 

 small, upwardly-pointing denticles on almost all the rays of the first dorsal 

 and caudal fins. The deeply-overlapping scales are ornamented with 

 elongated denticles of ganoine. The ossified air-bladder is conspicuous in 

 all fossils, its walls being formed of three paired longitudinal series of 

 large imbricating, bony laminae, each composed of a number of superposed 

 lamellae. The type species of Macropoma is M. mantelli from the Chalk of 

 S.E. England, attaining a length of about half a metre. The genus also 

 occurs in the Lower Chalk of Bohemia. 



FIG. 60. 



Undina gulo ; restoration, omitting scales and supraclavicle, about one-seventh 

 nat. size. L. Jurassic (L. Lias) ; Dorsetshire. The extent of the ossified 

 air-bladder is indicated beneath the notochordal axis in the abdominal 

 region. (From Brit. Mus. Catal.) 



The fins of the Ccelacanthidae are best understood from an 

 examination of the beautifully-preserved examples of the 

 Jurassic genus Undina (fig. 60). They are as already described 

 in Macropoma, with the addition of a minute supplementary 

 caudal fin, which has been observed in nearly all members of 

 the family. The endoskeletal supports of this fin, however, are 

 unknown. 



