472 EDWIN S. GOODRICH. 



In the majority of Teleostean fish the median and paired 

 fins are covered with a smooth scaleless skin, below which lie 

 the dermal fin-rays. For reasons which will appear later, I 

 propose to call these rays the lepidotrichia. They are, as 

 a rule, both jointed and branched. Generally they are 

 thicker and more rounded proximally, thinner and more 

 flattened distally. The jointing is usually more conspicuous 

 distally than near the base of the fin, where the divisions 

 may be obliterated, this region of the ray frequently becom- 

 ing rigid. By the more or less complete suppression of the 

 branching and jointing, the lepidotricliia may in many cases 

 become converted into the spines so often found in the fins of 

 the more modified Teleosts. 



The lepidotrichia, like the ceratotrichia, are present on 

 each side of the fins. Since they correspond from side to 

 side, fitting close together back to back, so to speak, they 

 form apparently single, but really paired rays, capable of 

 being split longitudinally into two. At the proximal 

 extremity the two elements diverge and closely embrace the 

 extremity of the median endo-skeletal fin-support. Here is 

 generally situated a small distal endo-skeletal element, the 

 so-called baseost, to which the dermal ray is firmly attached 

 by ligament. These structures have been well described by 

 Parker (29), Cole and Johnson (7), and Bridge (4). The 

 various pterygial muscles (m. erector, depressor, inclinator), 

 which are more elaborately differentiated than in the Elasmo- 

 branchs, spring from this proximal end of the fin-ray on 

 either side of the baseost (Text-fig. 4, p. 488). Such are tlie 

 typical structure and relations of the lepidotrichia in adult 

 Teleostean fish. They are always present, and throughout 

 the group they undergo no very essential change. 



Whereas in the caudal and paired fins the lepidotrichia 

 retain their primitive superiority in number over the endo- 

 skeletal rays (see p. 486), in the dorsal and anal fins they 

 correspond strictly to the latter in number and position. 

 Each double dermal ray in these fins articulates with the 

 extremity of one endo-skeletal fin-ray. 



