THE DEEMAL FIN- KAYS OF FISHES. 501 



transition from the rounded proximal segment to the more 

 flattened distal segments (fig. 45). 



On reaching the body the lepidotrichia are continued, each 

 in a single elongated piece which passes beneath the scales 

 and embraces the extreme end of the endo-skeletal fin-support 

 (fig. 5). In the living fish the rays probably overlapped a 

 certain amount of cartilage at the end of these bony endo- 

 skeletal rays. 



In Gyroptychius, which has preserved the ganoine covering 

 on its lepidotrichia, the segments have the appearance of 

 oblong shiny scales with a pitted surface. They closely 

 resemble the lepidotrichia of Osteolepis. Unfortunately, the 

 specimens I have examined are too fragmentary to allow of 

 an exact determination of the relation the proximal end of the 

 rays bears to the body-scales. Occasionally the appearance 

 of the rays is such as to lead one to believe that they are 

 formed, as Agassiz suggested for Palseoniscus (1, see p. 497), 

 of ganoid scales overlapping deeper dermal rays. Pander, in 

 fact, definitely states that this is the case not only in Gyro- 

 ptychius, but also in Osteolepis (27). The same idea is sug- 

 gested by some specimens of Rhabdolepis macropterus. 

 Nevertheless I believe that the rays are not really double, 

 and that the deceptive appearance is due to the breaking 

 away of the superficial bony layers together with the outer 

 ganoine. 



Hoi opt J child as. — Passing now to this last family of the 

 Crossopterygii, fish which, although they have preserved a 

 considerable amount of ganoine, have acquired cycloid over- 

 lapping scales, we find lepidotrichia of essentially similar 

 structure. In Glyptolepis the dermal rays closely resemble 

 in their general proportions those of Giyptopomus. The 

 lengthened proximal segment is perhaps a little shorter ; it 

 has no ganoine covering, and is of the same bony structure as 

 the deep layers of the body-scales (fig. 44). The exposed 

 jointed portions of the lepidotrichia are of similar bone, but 

 are provided with a ganoine surface. 



Holoptychius Flemingii is not well enough preserved 



