ON CERTAIN YERMIFOHM FOSSILS. 21 



crustacean, tlie species of wbicli was unknown to me, though in 

 general appearance it was not altogether unlike the common 

 sandhopper, but not quite so long. It was undoubtedly one of 

 the Ampliipoda. I soon took in this way five or six specimens, 

 all of the same species, and all forming tracks of precisely the 

 same character — namely, broad, slightly elevated, flattened, and 

 grooved. 



Whilst forming its track the animal is never seen ; it moves 

 along a little beneath the surface of the sand, which it pushes 

 upwards with its back, and the arch or tunnel thus formed 

 partially subsides as the creature passes forward, and, breaking 

 along the centre, the median groove is produced. 



I now turned my attention to the narrow or furrowed tracks, 

 and in the same manner took several specimens of another species 

 of crustacean, much smaller than the first, but bearing some 

 general resemblance to it. This species, like the former, makes 

 its track step by step, resting some little time between each 

 advance, but differs from it in having its back exposed to view 

 while moving ; on account of its colour, however, it is very diffi- 

 cult to distinguish from the sand. 



The captured individuals Avere placed in a shallow vessel, with 

 the bottom thickly covered with sand moistened with sea-water, 

 so as to resemble as nearly as possible the state of the beach 

 where the tracks are found, and I soon had the satisfaction of 

 seeing them make their tracks or runs in a state of confinement, 

 thus making assurance doubly sure. The tracks so formed 

 were precisely similar to those seen on the beach, but in one 

 instance an interesting modification was observed. I was watching 

 the movements of an individual of the larger species, when all at 

 once it thrust itself through the surface of the sand, and, sinking 

 immediately again, left there an oval swelling ; and repeating this 

 action five or six times, formed a series of nodules (PI. III. fig. 2,5), 

 which, if continued, would have produced a track of a j)eculiar 

 articulated appearance, much resembling, on a large scale, the 

 nodulous or beaded form already noticed as sometimes occurring 

 in a variety of the narroAv furrowed kind. 



