Manchester Memoirs, Vol. Ix. (1916), No. 2. 25 



a study of more satisfactory material will show that they 

 exist in other members of the group. In the meanwhile 

 their function must remain obscure. 



The elongated scales which have long been known to 

 occur behind the dorsal fins of the members of this group, 

 although they bear a superficial resemblance to the pelvic 

 spines, are certainly of very different significance, because 

 they form part of the general squamation and are not 

 free outstanding structures. They seem to have arisen 

 in the following way. Since the time of Egerton it has 

 been realised that there is a concentration of the endo- 

 skeletal supports at the base of the median fins shown for 

 example by the articulation of a number of radials with a 

 single basal element in the dorsal and anal fins of Tristi- 

 chopterus and Eustheuopteron. This concentration im- 

 plies an actual and real reduction in the width of the 

 insertion of these fins. As shown extremely clearly in 

 the specimen of Holoptychius which we have described, 

 the median fins are provided with a fleshy lobe whose 

 squamation is directly continuous with that of the body. 

 When the base of the fin is notched in from the back a 

 disarrangement of the squamation necessarily results, and 

 we hold that the elongated ridge scales have simply 

 grown forward to fill up the space so left. 



The very marked resemblance which exists between 

 the paired pelvic fins and the median fins in Holoptychius 

 suggests very strongly that they are of similar origin, and 

 that the median axis with paired radials which is the 

 characteristic " archipterygial " fin, and which occurs in 

 all Palaeozoic Crossopterygian fishes, has been formed by 

 a concentration quite similar to that which produced the 

 dorsal fin of Tristichopterus. It is difficult to imagine 

 that the primitive pectoral fin can have projected to such 

 an immense distance from the body and that it should 



