514 EUWIN S. GOODRICH. 



cycloid scales, and acutely lobate fins. Of all known fisli the 

 Holoptycbiidga would appear most likely to approach this 

 intermediate type. But the adoption of this theory meets 

 with serious difficulties. The presence of a proximal joint of 

 considerable length extending below the body-scales in some 

 Teleostomes (snch as Cheirolepis) is not easy to account for; 

 and the relation the inner ends of the ceratotrichia, campto- 

 trichia, and lepidotrichia bear to the muscles, connective 

 tissue, and eudo-skeleton, is so similar in all fish that it is 

 difficult to believe that all these rays have not been, at all 

 events partly, derived from some common form. 



According to the second and alternative theory, it may be 

 supposed that the camptotrichia of the Dipnoi have been 

 derived from the ceratotrichia of the Elasmobranchii, and 

 that they are overlaid with scales as the horny fin-rays are 

 overlaid with denticles. The jointing of the distal region 

 of the rays would follow on their ossification. On such a 

 view, it might be supposed that the lepidotrichia of the 

 Teleostomes have been formed b}^ the fusion of the original 

 dermal rays with the superficial scales in the distal region, 

 but not in the pi'oximal region, where the raj^s were deeply 

 embedded and remain unjointed. 



From a compound dermal ray so formed the lepidotrichia 

 of the higher Actinopterygii would be derived by the shorten- 

 ing of the proximal piece. The structure of the rnys of 

 Cheirolepis, and many of the Crossoptei'ygii (Holoptychiidae 

 especially), maybe takeu as strong evidence in favour of thi.s 

 second theorj^. But here, again, we meet with many diffi- 

 culties, such as the structure of the dermal rays of the 

 Osteolepidge, in which the proximal piece is scarcely deve- 

 loped. 



Between these two rival theories it is difficult, if not im- 

 possible, to choose in our present state of knowledge. I have 

 endeavoured above to give an impartial statement of the two 

 possible interpretations ; but it may be added that I am 

 strongly inclined to believe that the first theor}^ is the one 

 which is nearest the truth. 



