220 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 24, 



impressions of the outer prints may be seen on this ridge. The im- 

 pressions of the right side opposite the deeper part of the ridge are 

 unusually deep, and are more numerous and closer together than in 

 the shallower parts of the tracks. In no part of the series are the 

 impressions so distinct and well-defined as to allow a recognition of 

 the groups of threes repeating each other ; but in a few parts, as they 

 approach the deep excentric groove, the small innermost pits may be 

 observed. There are few places where two contiguous pits are divided 

 by an interspace equal to their own breadth. Although many of the 

 foot-prints on the same side are in pairs, more or less oblique, groups 

 of three occur not unfrequently. Nothing like claws or digital divi- 

 sions can be discerned where the impressions are deepest. The in- 

 termediate groove becomes shallow and gains the mid-space in the 

 last two feet of the present series. Where the impression is deepest 

 the tracks bend slightly in a different direction from the preceding 

 part, making about an angle of 162°. This deviation of the middle 

 impression would seem to indicate that it had been formed by some 

 appendage which continued to incline to the left after the body had 

 begun to bend to the right side, and the greater depth of the impres- 

 sion where the bend is greatest would show that there had been an 

 increased exertion on the part of the animal at the time of making 

 that bend. 



5. Frotichnites lineatus. PI. XIII. (|nat. size), and PI. VIII. A. 3. 



In a continuous track of the median impression, traceable along an 

 extent of 13 feet, this impression preserves in some parts for an extent 

 of between 2 and 3 feet a considerable and equable depth ; it is also 

 accompanied by a remarkable modification of the lateral impressions, 

 which are rather represented by continuous grooves than by a succes- 

 sion of pits, although these are suflSciently evident in many parts of 

 the lateral grooves, forming partial depressions in the grooves. Along 

 an extent of 13 inches, where the deep median impression is equi- 

 distant from the two narrow and shallow impressions on each side, 

 the outermost of these impressions is deepest on the left side, and 

 the innermost is deepest on the right : a little further on the lateral 

 grooves become broken up into a series of shallow foot-prints and 

 then again become continuous in shallow grooves. After an uninter- 

 rupted course of 5 feet from one end of this series of impressions, the 

 middle groove, after bending slightly to the right, terminates in a 

 point, the impressing part appearing there to have been raised ob- 

 liquely above the sand ; but the impression recommences to the left 

 and a little behind this point and somewhat more obtusely, and, again 

 becoming shallower, it seems to have been partially reimpressed to 

 the right of this, and then to have continued uninterruptedly, a little 

 varied in its depth, for some feet further. 



None of the impressions in this extent of tracks are sharply defined, 

 the borders both of the grooves and pits being much rounded off, as 

 if they had been partially effaced, either as having been made under 

 water, or by water having passed over them soon after they were 

 made. They give the idea of tbe animal having been partly sup- 

 ported by water whilst making them, so as to have occasionally 



