DJPN 



pf-t: 



small spine-like processes, highly characteristic (Fig. 200, B), and not 

 to be confused with denticles. This spiny covering is found in all 

 the living genera, and even in the Devonian Phaneropleuridae 

 ({Fig. 201) ; it is therefore an important and old-established form of 

 scaling, not found in any other sub-class. The trabecular and 



isopedine layers remain, 

 though in living genera 

 bone - corpuscles are no 

 longer present (Wieders- 

 heim [490]. Klaatsch 

 [264], Goodrich [178]). 



The dermal fin - rays 

 are always jointed, gener- 

 ally branched, and are 

 formed of a bon}- sub- 

 stance containing hone- 

 cells (Fig. 203). They 

 are slender, much more 

 numerous than the endo- 

 skeletal radials, with an 

 unjointed proximal piece 

 deeply emhedded in the 

 connective tissues 

 muscles, so as to 

 siderably overlap 

 radials [175]. In 

 modern degenerate Dipnoi 

 the dermal rays, or camp- 

 totrichia, become fihrous 

 and little calcified, thus 

 somewhat resembling the 

 ii the dorsal fin of ceratotrichia of Elasmo- 

 branchs. But in the early 

 fossils they are thoroughly 

 bon\ r , and approach lepi- 

 dotrichia in structure. The distal-jointed region of the camptotrichia 

 is, however, always covered over external^' by true scales ; and in 

 Dipterus these fit closely in rows along the rays (Figs. 202, 226). 

 It is, therefore, possible either that in Dipnoi we have lepidotrichia, 

 which have sunk deep below the surface, and been covered over by 

 a new set of scales ; or that the camptotrichia really are modified 

 ceratotrichia, with which the more superficial true scales are be- 

 coming associated. A still closer union of these two elements might 

 have given rise to the typical lepidotrichia of primitive Teleostomes. 

 Whatever may have been the history of the camptotrichia. they 

 differ considerably from the dermal rays of other fish [175]. 



.■C4C 



and 



con- 



the 



the 



Fig. -J02. 



Diagram of a section throu 

 Dipterus. ?>.«•, body-scales; dist.r, distal jointed region 

 of the camptotrich ; efr, radial of I'm ; pr.r, proximal 

 nnsegmented region of the camptotrich ; s.sc, scale ovei - 

 lying dermal ray. (From Qvart. Join n. Micr. s, i. ) 



