Mr. A. Hancock on Vermiform Fossils. 447 



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 spe- 

 cies of crustacean, much smaller than the first, but having some 

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

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

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

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

 ficult to distinguish from the sand. 



The captured individuals were 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 watch- 

 ing 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 re- 

 peating this action five or six times, formed a series of nodules 

 (PI. XIV. fig. 2 b), which, if continued, would have produced 

 a track of a peculiar articulated appearance, much resembling 

 on a large scale the nodulous or beaded form already noticed 

 as sometimes occurring in a variety of the narrow, furrowed 

 kind. 



Specimens of the two crustaceans which make these runs have 

 been submitted to Mr. C. Spence Bate ; and he obligingly informs 

 me that the larger one (that which makes the broad, elevated 

 tracks) is a scarce animal, and was described by him, under the 

 name of Bellia arenaria, in the ' Annals of Natural History ' for 

 1851 ; but the name was afterwards changed to that of Sulcator 

 arenarius. He alludes to its habit of making tracks in the sand. 

 The smaller animal he states to be an undescribed species of the 

 genus Kroyera, for which he proposes the specific denomination 

 of arenaria. Both species will be figured and described by that 

 gentleman in the i Transactions of the Tyneside Naturalists' 

 Field Club' for 1858. 



It has been already pointed out that the tracks, which we have 

 just seen are made by these crustaceans, are remarkably similar 

 to the vermiform impressions observed on the Carboniferous 

 slabs. Indeed, the broad raised track (PI. XIV. fig. 1) produced 

 by Sulcator arenarius so closely resembles some of the fossils, 

 that it is difficult to say in what they differ. The description 

 previously given of the former might, in fact, do very well for 



