1852.] OWEN POTSDAM SANDSTONE FOOT-TRACKS. 221 



dragged its lateral appendages along, and thereby to have made a 

 continuous groove with faint impressions, interrupted where the feet 

 have been applied to the sand in the usual successive way. 



The breadth between the outer margins of the outermost tracks is 

 5 inches 6 lines ; between the inner border of the innermost tracks 

 3 inches 10 lines ; the breadth of the median track is 10 lines. For 

 a short distance there is a shallow longitudinal depression on the left 

 border of the median track, and here and there are faint indications 

 of small impressions inside of the innermost of the lateral tracks. 

 The name indicative of this series of tracks is one of convenience only, 

 and is not to be regarded as the sign of a species recognized as actually 

 distinct from the differently-marked and better-defined impressions 

 of the same size and breadth. 



6. Protichnites alternans. PI. XIV. {\ nat. size), and 

 PI. VIII. A. 7. 



In a series of impressions in which the middle groove is represented 

 by a succession of interrupted shallow longitudinal channels, with 

 unimpressed or shghtly marked intervals of nearly their own extent, 

 the lateral impressions are deep, small, and more or less of an angu- 

 lar character. In some parts there appears only a single impression, 

 as at a on the left side, 1 2/ ; an inch in advance of this there will be 

 a pair, 5, V, placed rather obliquely, the innermost much larger than 

 the outer one. One inch and a half in advance of this is a third 

 more widely parted pair, c, c', also placed obliquely, the inner im- 

 pression being smaller than the outer one. Then at the same distance 

 follows a triplet, d, d\ c?', or a pair, d, d\ of nearly equal size, and on 

 the same transverse line, but wider apart than the rest. About 

 2 inches in advance of this is a pair, e, e, which are nearer together, 

 and then comes either a very large single impression or one com- 

 posed of a confluent pair, /. The outer impressions of the series de- 

 scribe a curve, with the convexity turned outwards, but the opposite 

 impressions of the series are not symmetrical ; for where the impres- 

 sions are widest apart on the left side, those of the right, as in 1 R^ 

 are nearest together, or, being confluent, appear single ; and where 

 the right pair of impressions are widest apart, those of the left side 

 are nearest together. The innermost impressions of both lateral 

 series preserve best their regular distance from the middle tracks. 

 The outer impressions differ most in this respect, and consequently 

 describe an undulating line, but so that when the convexity is turned 

 from the middle line on the left side it is turned to the middle line 

 on the right, and vice versa. Some of the innermost impressions are 

 elongated transversely and become gradually shallow outwards, as if 

 the foot impressing them had been moved from within outwards. 



These impressions indicate a waddling gait, or an alternate oblique 

 movement from side to side of the animal, with an alternate raising 

 and depressing of the part of the animal which has left the middle 

 impression. Here and there groups of three impressions are inter- 

 posed between the impressions in pairs. The shape of the impres- 

 sions indicates them to have been made by hard, pointed, subangular 

 extremities. 



VOL. VIII. — PART I. Q 



