﻿(XELACASTTHIDiE. 397 



neural arches and spines are long and slender, the two halves of 

 each arch being firmly united with their appended spine. In the 

 abdominal region, the hamial arches are delicate and rudimentary, 

 but in the caudal region they correspond in development to the 

 opposed neural elements. So far as known, these ossifications 

 extend only to the termination of the principal caudal fin, the 

 small supplementary caudal never displaying hard endoskeletal 

 structures. 



The paired fins are always well-developed and obtusely lobate. 

 The membrane-bones of the pectoral arch, though slender, are con- 

 spicuous, and seem to have been completely covered by the skin. The 

 long, gently curved clavicle often exhibits a robust post-clavicular 

 process, and articulates above with a small supraclavicle ; while a 

 long, slender infraclavicle overlaps its lower spatulate extremity. 

 The last-mentioned element curves sharply forwards and inwards, 

 terminating in a triangular expansion, where it meets its fellow of 

 the opposite side in a median suture (see PI. XIV. fig. 3, i. cl.). The 

 pelvic fins are supported by a pair of elongated, slender basipterygia 

 with an inwardly directed process at the distal end, by which they 

 are loosely apposed in the median line. 



• Of the two dorsal fins, the anterior is destitute of baseosts, the 

 stout dermal rays directly articulating with the nearly straight 

 upper border of the single laminar axonost. This fin therefore 

 exhibits no lobation. The posterior dorsal fin and the opposed anal 

 resemble the paired fins in being distinctly lobate. As in the paired 

 fins, the baseosts must have been too slightly ossified for preservation, 

 the lobe being always a vacant space in the fossils ; but there is a single 

 forked axonost to each fin, this almost invariably exhibiting a high 

 degree of ossification. The principal caudal fin is symmetrical, and 

 supported by a single series of long slender bones above and below, 

 equalling in number, and 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 sparse series of very 

 small rays fringing the supplementary caudal lobe, when present, is 

 probably in direct contact with the unossified spines of the axial 

 skeleton itself. None of the fin -rays are bifurcated, but all are 

 more or less articulated distally. 



A conspicuous feature in the abdominal region of all Ccelacanths 

 is the ossified air-bladder, which attains a large size, and sometimes 

 exhibits a single anterior aperture by which its internal cavity 

 communicated with the oesophagus. Its walls are formed of three 

 paired longitudinal series of large, imbricating, bony laminae, each 



