POLYCH.ETA. 



485 



Another fossil, which is extremely abundant in the Silurian rocks 

 of some localities, and which has generally been supposed to be the 





Fig. 349.— a, A small portion of the trail of Phyllodocitcs Jacksoni, from the Silurian slates 

 of Wurtzbach, of the natural size (after Geinitz) ; B, Small portion of the trail of Nereites 

 Loomisii. from the same locality, natural size (after Geinitz); C, Fragment of a slab, showing 

 Myrianites tenuis, from the Silurian slates of Thornilee, Peeblesshire, of the natural size. The 

 slab has split at different levels in different parts, and the fossil is seen to cut vertically across the 

 laminae of deposition, the surfaces thus formed being concentrically striated. (Original.) 



track of an Annelide, is Myrianites. In ordinary specimens of this 

 genus (fig. 349, c) all that is seen is that the surfaces of the strata 

 are marked by winding and tortuous linear impressions, of extremely 



