28 



PAL^ONTOLOOY OF NEW-YORK. 



The trail consists of a slightly elevated ridge in the centre, with a depression on each side 

 which limits it. This may have been produced cither by the moving body having two depressed 

 edges, with an arch between ; or it may have been made by some small object crawling beneath 

 the sand, elevating it in the centre, and thus causing a continuous depression on each side. This 

 trail, although presenting a general resemblance to that of Idotea, is nevertheless distinct, so far 

 as I have been able to observe the trails of that crustacean. 



Not only this, but numerous others of these tracks prove that the present inequalities of the 

 surface of the layers existed at the time the tracks were made. In more than one instance the 

 track is nearly obliterated in the depression, while, on the more elevated parts, it is perfectly 

 preserved. 



Fig. 1 6 is a similar trail, but smaller than the last. The small fragment figured is only a 

 portion of the surface of a large slab, which is similarly marked. In some instances the crossings- 

 and recrossings upon the same trail, in a small space and apparently by the same imlividual, ar6' 

 so numerous that it seems natural to suppose that the animal move<l rapidly. 



The Idotea before alluded to moves with considerable rapidity ; but the mollusca move 

 slowly, and it is not probable, therefore, that this trail is due to a gasteropod. The trails of 

 Melania, made on muddy and sandy bottoms beneath shallow water, are more similar in their 

 meandering direction and recrossings than the trails of JVatica, which are usually of no great 

 extent. The Melania, on the contrary, often leaves a trail of several feet long, winding about in 

 this manner j but the trail in this case is a simple depression margined by a slight ridge, pro- 

 duced by the animal pusliing away the material from before it, and pihng it up on each side^ 

 The tracks of Littorina on a sandy beach resemble these in some degree ; but they are usually 

 more direct, and show fewer recrossings in the same space. 



Figs. 2 a and 2 J. These are evidently trails of different character, presenting a simple 

 depressed channel without elevation along the centre as in the preceding forms ; and though 

 exhibiting different features from the ordinary wave-lines, are perhaps due to inorganic causes. 



Fig. 3 is a trail formed after the same manner as the preceding, in figures 1 a and 1 b, but 

 larger and stronger in its character. The continuation of the same trail occupies twice as much 

 space as represented in the figure. There is a slight imperfection in the centre of the specimen, 

 which has rendered the figure a little obscure : the whole is, however, a part of the same trail,- 

 which is continous in its windings throughout. 



Position and locality. This and the preceding specimens were found in Herkimer county, 

 in the raidne below Tisdale's sawmill. 



Fig. 4 is a large and very perfect specimen- of this kind of track. It has essentially the same 

 characters as the preceding ; but being so much stronger, and the depressions deeper, the effects 

 of the weight of the animal are quite distinct. The central ridge, with a depression on each side, 

 are not only very clearly preserved ; but on the outside of this, and beyond the depressed line, 

 the sand is piled up in a narrow ridge, as if in the progress of the animal the loose material had 

 been thrown out on either side. This is one of the most perfect specimens, and offers conclusive 



