500 EDWJN S. GOODRICH. 



same transition in form between the body-scales and the fin- 

 ray segments at the anterior edge of the fin (fig. 51). But as 

 a rule the distinction between the two is elsewhere marked 

 and abrupt (fig. 56). So far as I have been able to observe, 

 the proximal segment of the lepidotrichia of Osteolepis, 

 although generally longer than the others, lies flush with the 

 body-scales, and projects but very little below them. In the 

 nearly allied Diplopterus the proximal end of the ray may 

 be longer than in Osteolepis (fig. 56). 



The lepidotrichia of the Osteolepidfe are covered with 

 ganoine, and resemble closely the scales in histological 

 structure. 



Glyptopomidae. — Glyptopomus (Glyptolaemus) has thin 

 rhombic scales, ornamented with ganoine (Huxley, [19]). The 

 ganoine scarcely shows in the fossils on the fins, where it was 

 probably only feebly developed. The lepidotrichia differ from 

 those of the Osteolepidge in having a very much longer un- 

 jointed proximal segment, which was, perhaps, entirely, and 

 certainly was partially, covered with ordinary scales. These 

 scales become very thin and cycloid towards the periphery. 



Rhizo don t idee. — Eusthenopteron and its allies differ 

 from the Osteolepidge in having thinner, deeply overlapping 

 body-scales of more or less cj^cloid shape. Most of the genera, 

 excepting Gyroptychius, seem to have lost the coating of 

 ganoine on the lepidotrichia. 



Taking Eusthenopteron as a type, we find well-developed 

 lepidotrichia, freely branching and many-jointed (figs. 5 and 

 6). These rays are formed of bony substance, containing 

 bone-cells (fig. 43). The bone is laid down in concentric 

 layers in the proximal region, but as we pass towards the 

 periphery of the fin we find that the segments get more and 

 more flattened out, and become concave on their inner face. 

 The distal segments in section appear crescentic, like those 

 of modern Teleosts or Pholidophorus (figs. 45 a, b, and c). On 

 comparing sections taken at various levels of the dermal ray, 

 from within outwards, it will be seen that there is no funda- 

 mental difference between them, and that there is a gradual 



