494 EDWIN S. GOODRICH. 



exteusive bony skeleton, of scales and plates on the body, of 

 lepidotricliia and occasionally of fulcra on the fins, and of a 

 heterocercal tail, seems to support the old-fashioned view that 

 the forms included in the group Ostracodermi are really very 

 specialised offshoots from the Teleostome stem. A detailed 

 microscopic examination of their fins is urgently needed. 



The fins of Coccosteus seem to have been devoid of dermal 

 rays. 



We may now leave these imperfectly known and very 

 aberrant groups of fish, and pass directly to the consideration 

 of the Teleostomes. 



Although the various orders of fossil Teleostomi differ 

 from each other iu certain details of the structure of their 

 dermal rays, yet they all possess unmistakable lepidotrichia 

 of very uniform character. Only with respect to the proximal 

 end do the dermal rays exhibit any considerable divergence 

 of form. It will be most convenient to begin with those 

 extinct fish which are most nearly related to the surviving 

 groups of Teleostei, and to work back to the more primitive 

 forms. For this purpose we shall adopt the classification set 

 forth by A. Smith Woodward in his excellent British Museum 

 catalogues, and in his text-book (42 and 43). 



Actinopterygii. 



Isospondy li. — Amongst the great variety of fish included 

 in this group (the Teleostei and their earlier extinct relatives) 

 it is not until we reach the Leptolepidae that any important 

 change in the structure of the dermal rays can be observed. 

 In this family ganoine first appears on the surface of the rays 

 and scales. Not only have the OligopleuridjB and Pholido- 

 phorida3 a covering of ganoine on the lepidotrichia and bodj-- 

 scales, but rows of typical fulci'al scales are present at the 

 edge of their fins. Fig. 62 shows the lepidotrichia of 

 Pholidophorus in transverse section, and figs. Go and 04 are 

 drawn to illustrate the remarkable parallelism in histological 

 structure which occurs between the scale and the ray. The 



