322 MARKINGS, FOOTPRINTS AND FUCOIDS 



and sometimes, when the edges of the carapace touched the 

 bottom, with lateral furrows. In this way the animals were 

 able to swim with some ease and rapidity, and on one occasion 

 I observed an individual, confined in a tub of water, raise itself 

 from the bottom and swim around the tub at the surface in 

 search of a way of escape. Lastly, the young Limuli were fond 

 of hiding themselves by burrowing in the sand. They did this 

 by pushing the anterior rounded end of the carapace under the 

 sand, and then vigorously shovelling out the material from below 

 with their feet, so that they gradually sank under the surface, 

 and the sand flowed in upon them till they were entirely covered. 

 If carefully removed from the hollow they had made, this was 

 found to be ovoid or hoof shaped in form and bilobed, not un- 

 like the curious hollows (Rusophycus Grenvillensis of Billings) 

 which I have supposed to be burrows of Trilobites. 



I thus found that the common King-crab could produce a 

 considerable variety of tracks and burrows comparable with 

 those which have been named Protichnites, Climactichnites, 

 Bilobites, Cruziana, Rusichnites, etc. ; and that the kind of 

 markings depended partly on the differences of gait in the 

 animal, and partly on the circumstances in which it was placed ; 

 so that different kinds of tracks do not always prove diversity 

 in the animals producing them. 



The interest of this investigation as applied to Limulus is 

 increased by the fact that this creature is the near ally of 

 Trilobites, Eurypterids and other Crustaceans which were 

 abundant in the earlier geological ages, and whose footprints 

 are probably among the most common we find on the rocks. 



Lastly, on this part of the subject, it is to be observed that 

 many other marine animals, both crustaceans and worms, make 

 impressions resembling in general character those of Limulus. 

 In addition to those already mentioned, Nathorst and Bureau 

 have shown that various kinds of shrimps and lobster-like 

 Crustaceans, when swimming rapidly by successive strokes of 



