FINS or GANOIDS AND TELEOSTS. 551 



and each consists of a proximal (p.s.) and a distal (d.s.) segment. 

 Each proximal segment is broad above, but becomes slender and 

 tapering towards its inner extremity. For the upper half of its 

 extent the segment suturally articulates with its fellows in front 

 and behind by straight or slightly curved anterior and posterior 

 margins, while the distal extremity is somewhat expanded laterally 

 and, at the same time, produced obliquely upwards and backwards 

 into an abruptly truncated " postero-superior " process (ps.p.) 

 which articulates with the distal segment, and almost precisely 

 resembles a confluent mesial segment both in its relations to the 

 distal segment and in its mode of articulation with the antero- 

 superior margin of the next succeeding proximal segment. The 

 postero-superior process and the adjacent anterior portion of 

 the distal end of the segment furnish a smooth concave surface 

 for articulation with the base of a fin-ray. The distal extremity 

 of the proximal segment of the last radial element is produced 

 backwards into a thick lamina of bone, which may possibly 

 represent one or more fused segments. 



The distal segments are simple osseous nodulesc Interossicular 

 ligaments extend from the upper surface of the postero-superior 

 process of each proximal segment to the distal segment, and from 

 the latter to the postero-superior process of the next succeeding 

 proximal segment. 



The first three radial elements {r.e}-r.e.^) differ somewhat from 

 the others. They are more or less firmly united together by 

 suture throughout their entire length, and are otherwise modified 

 for the support of the large defensive spine and the smaller 

 spine in front of it — the " guard-spine " — which provides for the 

 support and fixation of the defensive spine in the erect position. 

 The first (r.e?) includes only a proximal segment (p.s.), and is 

 represented by a somewhat triangular bony plate with the apex 

 directed forwards and its base firmly attached by suture to the 

 proximal segment of the second. Distally, the plate is produced 

 outwards into two prominent lateral ridges. The second also 

 consists only of a proximal segment (r.e.\ p.s.) similar in shape 

 to those which succeed it, but terminating distally in a projecting 

 process (p.), provided with a smooth anterior surface, for the 

 support of the " guard-spine " {g.sp.). Distally also, but at a 

 point anterior to the projecting process already mentioned, the 

 lateral margins of the segment are produced outwards and back- 

 wards in such a way as to form a horizontally disposed V-shaped 



