560 PROF. T. W. BRIDGE ON THE MESIAL 



cartilage-tipped extremity, provided with two flat oblique surfaces 

 meeting at an angle. The distal segments (d.s.) are all carti- 

 laginous, somewhat plano-convex in shape, and intercalated 

 between the distal ends of the proximal segments in such, a way 

 that tbe convex inferior surface of eacb articulates with two 

 oblique surfaces furnisbed by tbe distal extremities of two con- 

 tiguous proximal segments. Towards the anterior and posterior 

 extremities of the fin, the distal segments to some extent lose 

 their usual intercalated arrangement and become more directly 

 related to the distal ends of the proximal segments to which they 

 belong. 



All the fin-rays are cleft basally and clip the distal segments 

 of their supporting radial elements. 



Anal Jin. — In the structure and disposition of its radial elements 

 the long anal fin closely resembles the dorsal. 



acakthoptertgii. 



Bertcid^. 

 Solocentrum spiniferosum. 

 Dorsal fin. — The dorsal fin consists of an anterior spinose 

 portion and a posterior section consisting of soft multiarticulate 

 fin-rays. There is, however, no interruption in the sequence of 

 either the fin-rays or the supporting radial elements, Twenty-five 

 radial elements (PI. XXII. fig. 21, r.e.^-r.e.'^") are present, of which 

 the first ten support eleven stout spines, the remaining fifteen 

 supporting sixteen soft rays. The ten spine-bearing elements 

 (r.(?.--r.e.") are bisegmental, each consisting of a dagger-shaped 

 proximal segment (p.s.) with well-marked lateral longitudinal 

 ridges, and, in addition, a distal segment (d.s.). Each proximal 

 segment has at its distal end (i.) an anterior facet for arti- 

 culation with the distal segment of the radial element immediately 

 anterior to it ; and (ii.) behind the facet a transversely disposed 

 articular surface for the condylar base of a fin-ray. Posteriorly 

 to this the distal end of the segment contracts somewhat, and then 

 widens out into two transversely disposed lateral wings (fig. 22, 

 jo.s.) which are directed upwards as well as outwards, and, in 

 conjunction with similar wings developed from the distal seg- 

 ment (d.s.), form a section of a well-marked medio-dorsal bony 

 groove extending the whole length of the spinose portion of the 

 fin, and serving for the reception of the spines when the latter 

 are deflected. The lateral notches («) which are to be seen 



