Dawson on the footprints of Limultis, 



273 



the sand, but occasionally moved slightly from side to side, or up 

 and down, in such a manner as to make a broken, irregular trail. 

 When the creature turned abruptly, the impressions on the inner 

 side of the curve were much stronger than those on the outer, 

 and the tail mark became more irregular, or was drawn toward 

 the inner side. Occasionally the spines on the sides of the abdo- 

 men touched the ground, and produced slight longitudinal 

 scratches among the footprints. These appearances are repre- 

 sented in Fig. 1, reduced to one-third of the natural size. 





As compared with Proticlmites these tracks of the Limulus 

 agree in the median groove, and in the regularity of the suc- 

 cessive groups of impressions at the sides ; in reference to which 

 the track of Limulus might be named if it were a fossil, '' Ichnites 

 quatuor-iiotatus ;^' and it is to be observed that in Limulus the 

 regularity of the impressions results from the use of a pair of 

 limbs divided into several strong points at their free extremities. 

 The principal diflference is in the lateral grooves, which do not 

 appear in Protichnites, and in the less proportionate size of the 

 impressions of the feet, and the smaller number in each series. It 

 is however to be observed, that my specimen was a small animal, 

 giving an impression only 4 inches wide, and that a full grown 



Can. Nat. 18 Vol. VII 



