ON DORYPTERTJS HOFFMANNI. 253 



extends a longitudinal transversely elongated plate (figs. 1, 2, g) 

 inclined backwards, the largest of which measures about a quar- 

 ter of an inch in length ; these, which we shall call the lateral 

 plates, are expanded and bifurcated (g') in the direction of the 

 length of the fish at their inner extremities, and thus embrace, 

 as it were, the lozenge-formed areas or plates bearing the ridges 

 already described ; or perhaps this arrangement would be better 

 described by stating that the forks of the opposed plates, meet- 

 ing on the median line, form the lozenge-shaped areas or plates, 

 to which they give an elevated border. The lateral plates have 

 a boss-like enlargement at the point of bifurcation ; here the 

 plates are narrowest ; hence they widen gradually for some dis- 

 tance, and then, turning backwards, taper to the termination. 

 The margins are abruptly defined, and are slightly elevated into 

 narrow ridges, which die out towards the outer margin. The 

 bifurcations of the adjacent plates are in contact ; and so are the 

 outer terminations. But for the rest, the plates are divided by 

 a lanceolate space. The tapering distal or outer extremities of 

 the lateral plates are united each to a stoutish rod (?'), which at 

 the point of union is cylindrical and somewhat enlarged. These 

 are slightly arched backwards and inclined considerably in the 

 same direction ; their outer extremities are a little widened, 

 flattened, and grooved longitudinally ; and, suddenly contract- 

 ing, they turn forwards, and each becomes joined to the inner 

 pointed extremity of a sigmoidal ridge-like plate ( j), which rises 

 boldly up, and which, inclining much forward, terminates in a 

 recurved sharp point a little within the general margin of the 

 fish. The sigmoidal ridges gradually widen in the centre, where 

 there is a longitudinal groove ; and they, as well as the rods, 

 are divided from each other by a considerable space. Such is 

 the general appearance of these sigmoidal ridges or plates ; but 

 on closer examination the ridges are found to be formed of the 

 turned-up edges of wide flat sigmoidal plates (/), which extend 

 from ridge to ridge. 



Such is the description of the transverse series of plates and 

 rods of the posterior half of the body, numbering sixteen or 

 seventeen, corresponding to the caudal vertebrae, to which the 



