MARKINGS, FOOTPRINTS AND FUCOIDS 319 



the most prolific source of markings on sea-formed rocks. 

 Sometimes they cover very large surfaces of these, or penetrate 

 the beds as perforations, with tortuous furrows, or holes per- 

 fectly simple, or marked with little striae made by bristles or 

 minute feet, sometimes with a fringe of little footmarks a 

 each side, sometimes with transverse furrows indicating the 

 joints of the animal's body. Multitudes of these markings 

 have been described and named either as plants or as worm- 

 tracks. Again, these creatures execute subterranean burrows, 

 sometimes vertical, sometimes tortuous. These are often 

 mere cylindrical holes afterwards filled with sand, but some- 

 times they have been lined with a membranous tube, or with 

 the rejectamenta of the food of the animals, or with little 

 fragments of organic matter cemented together. Sometimes 

 they open on the surface as simple apertures, but again they 

 may be surrounded with heaps of castings, sometimes spiral 

 in form, or with dumps of sand produced in their excavation, 

 and which may assume various forms, according to circum- 

 stances. Sometimes the aperture is double, so that they seem 

 to be in pairs. Sometimes, for the convenience of the animal, 

 the aperture is widened into the form of a funnel, and some- 

 times the creature, by extending its body and drawing it in, 

 surrounds its burrow with a series of radiating tracks simulat- 

 ing the form of a starfish or sea anemone, or of the diverging 

 branches of a plant. 



Creatures of higher grade, provided with jointed limbs, 

 naturally make their actions known in more complicated ways. 

 Some years ago I had the pleasure of spending a few weeks 

 at the favourite sea-side resort of Orchard Beach on the New 

 England coast, and there made my first acquaintance with that 

 very ancient and curious creature the Limulus, or Horse-shoe 

 Crab, or King-crab, as it is sometimes called. Orchard Beach 

 is, I presume, near its northern range on our coast, and the 

 specimens seen were not very large in size, though by no means 

 1 6* 



