THE LONG-SNOUTED CHIMAEROID OF JAPAN. 13 



the fused neural plates of the original .segments whose presence is 

 attested by the distinct openings for the exit of spinal nerves. This 

 great expansion of the neural elements has probably been concomitant 

 with the evolution of an erectile dorsal fin which required a firm 

 hinge for its anterior spine. The disposition of the muscles which 

 erect and depress the fin bespeak a thinning away of the median 

 portion of this neural plate, and the thickening of its anterior margin. 

 Further examination of this portion of the column gives no evidence 

 that discrete centra, in the elasmobranchian sense, are represented. 

 The cartilage which encases the sides of the notochord can in this 

 form best be interpreted as coalescence of the neural and haemal 

 cartilages, a coalescence apparently the result of a specialization of 

 structures for supporting and operating the dorsal fin. 



Unpaired Fins. PI. I, Fig. 4. 



The series of dorsal fins is more clearly marked than in 

 Chimaera. The first dorsal fin is separated from the second by a low, 

 extended and ray less fold of integument. The second dorsal, which 

 presents a rounded upper margin, bears a series of close-set dermal 

 rays. This again is separated by a considerable interval from the 

 dorsal lobe of the caudal fin. In this lobe, which is somewhat adipose, 

 dermal rays are present, but are inconspicuous. The first dorsal fin 

 dossesses the basal support usual in chimaeroids. Its dermal rays are 

 drawn together into about half a dozen strong supporting elements of 

 the fin web, as shown in the figure. The anterior spine is slender 

 and remarkably delicate ; its tip, in fact, is broken off in all but two 

 of the specimens examined. And it is in the tip, only, i. c, in the 

 upper third of the spine, that a postero-lateral marginal serration 

 occurs. The " denticles " are here minute and disposed somewhat 

 irregularly. The surface of the spine is ornamented with a few 



