256 MESSES. HANCOCK AND HOWSE 



portion of the dorsal fin, and form part of an extended series 

 that reaches to the root of the tail- The broad plate inclining 

 forwards, and in continuation of the lateral plates, is undoubt- 

 edly a modification of the rod of the posterior part of the body ; 

 its margins are abrupt and produced into slightly elevated 

 ridges ; and it contracts a little towards its outer extremity, and 

 is slightly thickened at this point. The next portion, which in- 

 clines backwards, appears to represent the sigmoidal ridge or 

 plate. The margins of this portion of the series are in contact, 

 and seem to be slightly imbricated ; and the outer extremities 

 are turned a little forwards to become united to the external 

 hour-glass-shaped plates. 



In the transverse centre of these modified sigmoidal plates 

 there is a ridge (i"), similar in appearance to that on the me- 

 dian lozenge-shaped areas. This upper series of ridges forms a 

 line which extends from the nape, a little above the commence- 

 ment of the lozenge-shaped areas, and, passing backward pa- 

 rallel to them and about midway between them and the dorsal 

 margin, terminates immediately behind the anterior elongated 

 portion of the dorsal fin. This line of ridges resembles the up- 

 per line of mucus-tubes in Polypterus (' Poissons Fossiles,' t. ii. 

 pt. 2. p. 50) and in Dapedius punctatus (ibid. t. ii. p. 192, pi. 

 25 a) ; and, indeed in the latter, which in form closely resembles 

 Dorypterus, this upper or second lateral line, according to Agas- 

 siz, holds relatively exactly the same position. 



The marginal hour-glass- shaped plates have their sides abrupt 

 and slightly elevated into ridges. A similar ridge passes along 

 the centre ; and the most contracted part of the plate is thick- 

 ened or elevated, the ends becoming depressed and thin. These 

 peculiar plates, we have said, form a portion of a marginal series 

 (fig. 1, k) that reaches to the root of the tail. Behind the ante- 

 rior or elevated division of the dorsal fin they are much reduced 

 in size, diminishing backward in length in proportion to the re- 

 duced height of the fin, and are not connected with the sigmoidal 

 extremities of the transverse series of plates and rods ; neither 

 do their outer extremities appear to articulate with the fin-rays, 

 though there are pretty regularly two rays to each plate. The 



