Fio. 30. 1. Rill-mark (after Williamson). 2. Trail made by a seaweed 

 dit,gged along a soft plaster of Paris surface (after Nathorst). 8. Tracks 

 made by Goniada maculata, a Polychaet (after Nathorst). 4. Burrow 

 of an insect. 4 a. Section of the gallery (after Zoiller). 



