THE DEVONIAN PERIOD 579 



The ancient ganoids usually had cartilaginous skeletons and bony 

 scales, while the modern teleosts have bony skeletons and mem- 

 branous scales. The fishes of the time seem to have been more 

 fully clothed with spines and defensive armor than those of recent 

 times. Compared with the existing species, they were doubtless 

 heavy, clumsy, and sluggish. From the degree of development 

 already attained, it may be inferred that the ancestors of these 

 fishes had been living for a long time in the originating tract, prob- 

 ably somewhere in the north, for, as noted, they do not appear in 

 the Helderberg and Oriskany faunas of the southeast. It is not 

 improbable that fish were inhabitants of the northern seas from 

 Silurian times onward. Some of the American species of arthro- 

 dirans and sharks have been found in Spitzbergen, and others in 

 Germany. 



Another significant feature of the Onondaga fauna was the 

 profusion of corals. From the rapids of the Ohio at Louisville, 

 more than 200 species have been collected, embracing both the 

 simple cup form (a, Fig. 416) and the compound type. Some of the 

 cup corals attained a length of 18 inches and a diameter of 3 inches, 

 but the range in size was great, small and large forms intermingling. 

 The reef-building habit attained greater development than in the 

 Silurian times, the reef at the rapids of the Ohio being the most 

 famous example. In view of the abundance of the corals, it is 

 rather singular that the crinoids were rather few, since both forms 

 usually find clear, warm waters congenial. The crinoids, however, 

 do not appear to have lost their vitality, for they appeared in 

 abundance later. Very likely they may have been .depressed by 

 some hostile organic influence. Cystoids have not been found. 

 They were far down their declining curve toward extinction. Blas- 

 toids were present (b, Fig. 416) but other echinoderms have not been 

 found. Brachiopods formed an important part of the fauna, many 

 of them being large and giving evidence of congenial conditions. 

 In contrast with the Helderberg and Oriskany faunas, cephalopods 

 were abundant. It will be remembered that in the primitive types 

 of the cephalopods, the septa of the shells were plane or symmet- 

 rically curved, and that their juncture with the outer shell was a 

 simple curve. In the Onondaga epoch one form had septa which 



