32 ON CERTAIN VERMIFORM FOSSILS. 



wise states, from a slaty hazle just above the little limestone. 

 It is, therefore, of no great moment that trilobites have not 

 been found in the strata from which these vermiform fossils are 

 obtained, since they have been procured from the associated beds. 

 And it is a remarkable fact, that no remains whatever of any 

 organic body are found in these flagstones; yet, is there not 

 sufficient evidence to prove that life abounded in the seas from 

 which these rocks were derived ? Numerous trilobites might 

 have existed during their deposition, and may have perished 

 with the other inhabitants of those seas, leaving no trace behind 

 them except these, as it were, footprints in the sand. Many 

 such footprints are all that is left in the world's stony record of 

 existences that have passed away, and so it may be with these 

 fossil tracks. 



The carboniferous trilobites, however, correspond very well in 

 size to the tracks, — the largest of the grooved kind of which is, 

 we have seen, a little above an inch wide. The width of the 

 pygidium of Phillipsia truncatula is stated to be eleven lines ; 

 that of the cephalic shield would probably be a little more. 

 Therefore, if allowance be made for the thickness of the tunnel- 

 wall, and the necessary enlargement of the calibre beyond the 

 width of the animal, it is evident that, so far as size is concerned, 

 the largest tracks might be attributed to this species. 



The nodulous tracks are not more than half ,an inch wide. 

 There can, therefore, be no difficulty as to size with respect to 

 this form. The P. gemmulifera has the pygidium five lines wide; 

 so has Griffitliides calcaratus, and two or three other species are 

 described to be about the same size. And, moreover, the large 

 cephalic shield, with its anterior or bead-tubercle (glabella), and 

 projecting " cover of the eyes," appears well calculated to plough 

 its way beneath the surface of the sandy or muddy beach. And 

 it is worthy of remark, that in some of the tracks the central por- 

 tion is considerably elevated, forming the upper surface or roof into 

 three areas — a central elevated portion (PI. VIII. fig. 2, a), and 

 two comparatively depressed lateral portions (c, c). The former, 

 which appears to correspond to the glabella, is grooved (b) along 



