ANNELIDA. 325 



shape, with a median groove, often intricate and convoluted, 

 sometimes knotted, and several feet in length; (2.) Narrow 

 wedge-shaped furrows, 2-10ths of an inch wide, winding 

 capriciously and often abruptly over the surface ; (3.) Nodu- 

 lated or articulated tracks, consisting of a small furrow, with 

 a rounded ridge on one side. Mr Hancock showed that 

 tracks of these three kinds are actually produced "by the 

 above-named small Crustaceans, which burrow beneath the 

 sand, but a short way below the surface, " the arch or tunnel 

 thus formed partially subsiding, as the creature moves for- 

 wards, and breaking along the centre," thus giving rise to a 

 median groove. There is no doubt that the phenomena so 

 carefully observed by Mr Hancock throw considerable light 

 upon the subject of the supposed Annelide tracks of muddy 

 and sandy sediments ; but there is room for much hesitation 

 before concluding that any of these tracks, in the older 

 rocks at any rate, were really formed by Crustaceans like the 

 living Sulcator arenarius. One ground for such hesitation 

 need alone be brought forward here namely, that the so- 

 called " Annelide-tracks " of the older Palaeozoic rocks often 

 occur in vast numbers, in finely-levigated deposits, and through- 

 out a thickness of sometimes hundreds of feet of strata, and 

 that it is almost inconceivable that traces of the makers 

 should not have been detected in the same beds, supposing 

 them to have been formed by animals, which, like Crusta- 

 ceans, have a skeleton highly susceptible of preservation in 

 the fossil condition. 



Principal Dawson, again, suggests " that Algae and also 

 land-plants, drifting with tides and currents, often make the 

 most remarkable and fantastic trails," which might easily be 

 mistaken for the tracks of Annelides. This suggestion is a 

 very valuable one, but certainly will not explain the origin 

 of the majority of the so-called " Annelide-tracks " of the 

 Palaeozoic rocks, the regular serpentine form of which is one 

 of their most remarkable features. The same distinguished 

 authority remarks that " Lingulae, when dislodged from their 

 burrows, trail themselves over the bottom like worms, by 

 means of their cirri," and that " colonies of these creatures, 

 so abundant in the Primordial, may, when obliged to remove, 



