PACKARD. — PALEOZOIC ARTHROPOD TRAILS. 



65 



footprints were slightly oblique series of four punctures, or pits, " deepest 

 behind, in which the four marks left by the nails of the posterior feet 

 were most prominent, and sometimes the only marks seen." 



FiGUKE 1. 



Figure 2. 



" When the Limulus creeps on quicksand, or on sand just covered 

 with water, so that its body is partly water-borne, it appears principally 

 to use its ordinary walking feet, and the footprints then resolve them- 

 selves into a series of longitudinal scratches after the manner of Protich- 

 nites I meatus" . . . 



" When placed in shallow water, just covering the body, the creature 

 used its flat abdominal swimming feet, and though the impression made 

 was very faint, and not readily observed under water, it was obviously 

 very different from those before mentioned, agreeing with them only in 

 the lateral and median grooves, while between these were series of fur- 

 rows extending obliquely from each side of the middle groove, and re- 



VOL. XXXVI. — 5 



