480 EDWIN S. GOODRICH. 



Dipnoi. 



Ceratodus seems to be the only Dipnoan of which the 

 dermal rays have been described in any detail. Giinther (12)^ 

 in his well-known memoir on the Australian lung-fish, gives 

 the following- account of the dermal rays, which he calls the 

 " dermo-neurals " and " dermo-hcBmals " : — "They are ex- 

 ceedingly numerous^ four or five or more corresponding to a 

 single vertebral segment, and form a double series, one series 

 on each side of the fin. This peculiarit}", which Ceratodus 

 has in common with Lepidosireu, reminds us of those fin-rays 

 of Teleosteous fishes which can be more or less completely 

 split into a right and left half. The dermo-neurals of Cera- 

 todus are not articulated to the extremities of the inter- 

 neuralsj but overlap them for a considerable distance of their 

 length. . . . No ossification takes place in either of them ; 

 they consist entirely of cartilage in which numerous spindle- 

 shaped cells are embedded, man}^ of these cells being pro- 

 duced at both ends into a very long process." Giinther 

 evidently considered the dermal rays of Ceratodus to be 

 simple, uujointed, and unbranched, since he contrasts them 

 Avith the jointed and branched rays of Dipterus. 



The structure of the dermal rays of the Dijmoi is so im- 

 portant from the point of view of classification that it is 

 necessary to discuss the subject in detail. 



In the adult Ceratodus the median fins pass gradually into 

 the body; there is no sharp line of demarcation between the 

 two. The body-scales extend evenly on to the fin, where they 

 become smaller, more numerous, and of a more elongated 

 shape (fig. 3). The more distal scales become ranged in rows 

 parallel with the underlying dermal rays, but not strictly 

 corresponding to them. The scales do not reach the actual 

 margin of the fins, ceasing some little way short of it. 



These scales are, of course, covered by the epidermis, and 

 lie embedded in the connective tissue where they are formed. 

 Below the scales, and therefore in the still deeper layers of 



