LETTER TO AGASSIZ. 145 



was a slight curve in each, like that of an elbow a very 

 little bent. 



' I can say almost nothing regarding the head of the 

 animal. Almost all the specimens I have yet found 

 show it variously. In some the fossil has a decapitated 

 appearance, in others there are faint markings which 

 merely show that a part of the creature extended above 

 the arm-like fins, while yet a third kind shows a toler- 

 ably well-defined head. But even in specimens such as 

 the last all is obscure. Among the detached plates, 

 however, I occasionally find one of a peculiar form which 

 seems to have covered the upper extremity of the animal. 

 In shape it somewhat resembles the snout of a ray. It 

 is arched transversely, and a longitudinal depression 

 runs through the centre, beginning a very little from the 

 point. All my specimens of this plate are rather too 

 weighty to send you, but Dr Malcolmson writes me that 

 one which I picked up for him you have brought with 



you to Neufchatel In specimens 5, 6, and 



7 you will find the remains of a small fish a contempo- 

 rary of the tuber culated one. Unlike the fish with a 

 single large spine in each fin which I find in the same 

 beds, it was furnished with teeth. The fins, too, were 

 not scaled like those of the other, and instead of being 

 fastened to single spines, somewhat like the sails of a 

 boat to the yards, the membrane of each fin seems to 

 have been supported in the commoner way by a num- 

 ber of rays. I find a striking difference, too, in the 

 appearance of the head ; the bones are strongly mark- 

 ed, and the external surface much roughened; whereas 

 the head of the fish with the spines has always a 

 smooth, flat appearance, except at the neck, where 

 what seems to have been the gills, or perhaps rather 

 a sort of fringe which overlapped these, may be 



VOL. II, 10 



