166 OUR COMMON BRITISH FOSSILS. 



near Douglas, in the Isle of Man, there may be 

 frequently found the tracks of two kinds of sea- 

 worms, Nereis and Nemertites. As before remarked, 

 however, the Longmynd rocks afford by far the largest 

 number of evidences of ancient sea-worms. In the 

 Wrekin the quartzite beds yield Arenicolites Urico- 

 niensis, which may be considered the oldest known 

 British fossil. The rocks of St. David's contain both 

 Arenicolites and Serpulites. In the Skiddaw slates, 



Fig. 134. Burrow of Histioderma Hibernicwn. 



near Keswick, Cumberland, ten species of the remains 

 of fossil-worms have been catalogued, among which 

 Scolithus and Helmintholitkus are the most abundant. 

 One remarkable species has been named Stellascolites. 

 In many parts of Great Britain the lower Carboni- 

 ferous rocks possess most abundant traces of worm- 

 tracks. Any tourist who has visited the magnificent 

 Cliffs of Mohr, in county Clare, Ireland, cannot fail 

 to have noticed the dark slaty flags of the district, 



