

^^ 



36 



PAL^ONTOLOCrY OF NEW- YORK. 



Fig. 4 is a part of the same slab ; and the two double ranges of tracks commencing at a^ 

 proceed with varying distinctness to h : here they are obliterated by a depression in the stone,- 

 evidently a kind of water-course ; after which they are again visible some four or five inches 

 beyond, as represented in fig. 3, commencing at c. 



The whole extent of these lines of tracks is more than twelve inches ; and they are of uniform ^ 

 size and character throughout, except from abrasion due to subsequent action. This fact appears 

 to me to be an argument against their hating been appendages of a cephalopod, which, in so 

 great a length, would have presented some variation in size. j(^ 



Fig. 5 is a portion of another slab of similar character with the last. The tracks are here also 

 partially obliterated by a shallow water channel. This specimen^ like the last one, exhibits some 

 impressions with no distinct trace of appendages ; showing that such absence, in other cases,- 

 depends upon subsequent abrasion, or upon the power of the animal to make impressions -with ^^ 

 the appendages closed. ^^^ ^ 



Fig. 6 represents a portion of a specimen with small pitted tracks on one side, and on the 

 other are the meandering continuous trails previously noticed. In the small pitted tracks a few* 

 of them are distinctly digitate, while others are apparently simple impressions. This circumstance 

 renders it difficult to distinguish betw'een species. ^^ 



■^ V- ^ 



PLATE XVI. Figs. 1, 2, 3, 4. J ^ 



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Fig. 1 presents several series of tracks differing to some extent from each other. The lefthand 

 double series are confluent in the lower part, though a careful examination shows them to have 

 been made by two limbs or other appendages. In the upper part they become separated, showing 

 two distinct ranges, the impressions being individually tridactyle. The middle range, in its 

 commencement near the base of the specimen, seems to have been made by a sharp claw planted 

 at the upper righthand extremity of the track, and then drawn obliquely downwards, and agaiii 

 more transversely. They are distinct sharp impressions, and have been made with force, as the 

 surface is depressed towards them on both sides. Toward the upper part of the specimen, these 

 tracks assume the character which the first range have near the lower part, and seem as if made 

 by two limbs impressed together upon the sand. The righthand partially double range presents 

 a somewhat different appearance. These, like the others, appear to have been made by a sharp 

 claw planted at the upper angle and drawn obliquely downwards, accumulating a distinct sharp 

 knob or ridge of sand below it as shown in the figure. The evidence that the impressions were 

 made in this manner is very clear : no other cause, than a body in motion, could have produced 

 such sharp pits with the accumulation of sand behind. An inspection of the specimen convinces 

 one that they must have been made on wet sand ; and to be assured of this, we have only to 

 strike a sharp point or hook into moist mud or sand, draw it a short distance, and then withdraw 

 it without obliterating the little pile of mud or sand which has accumulated before it. 



Fig. 2. This specimen presents all the characters of the last combined. There appears to be 

 two double ranges of tracks. The lower parts of both are partially obliterated, not by water^ 



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