272 Dawson o?i the footprints ofLimulus, 



tained a living Limulus,* it occurred to me to observe the nature 

 of its footmarks, and to compare these with the ancient Prot- 

 ichnites. The Limulus frequents this beach, which in its appear- 

 ance and character is probably not imlike the sandy flats repre- 

 sented by the Potsdam sandstone, in the spring, for the purpose 

 of spawning, and in storms many of them are cast on shore. In 

 summer they are more rare, and my specimen was a small indi- 

 vidual taken in a pool of salt water near the mouth of the Scar- 

 borough river. I had no means of preserving permanent impres- 

 sions of its footprints, but tried its mode of locomotion under 

 various conditions on the sandy shore, and preserved sketches of 

 the markings. 



The Limulus is provided with three sorts of locomotive appa- 

 ratus. In the male three pairs, and in the female four pairs of 

 the thoracic feet are didactyle, walking and prehensile feet^ 

 serving for locomotion on hard bottom under water. The poste- 

 rior pair of thoracic feet are longer and stronger than the others, 

 and furnished, in addition to a small didactyle foot, with four 

 broad, flat claws or nails, which when spread out and pressed 

 against the surface, enable the creature to move on the moist 

 sand of the shore, and also to scoop out the sand and force itself 

 beneath the surface in burrowing. Lastly, the flat abdominal feet 

 are used for swimming, and with the aid of these the creature 

 could rise to the surface and swim around a pail in which it was 

 kept. Its motions were not rapid, and its principal means of 

 security seemed to be burrowing under the sand, and when touched 

 doubling up the abdomen under the thorax in the manner of a 

 Trilobite, though less perfectly, and at the same time erecting and 

 brandishing the sharp caudal spine. 



When laid on damp sand near the margin of the sea, the crea- 

 ture immediately began to walk, but in a circuitous manner with- 

 out apparent object. Its body rested upon the edges of the 

 broad cephalo-thorax, as on a pair of sleigh runners, and it urged 

 itself forward principally by the two posterior feet. The impres- 

 sions made consisted of two distinct furrows, with slight ridges 

 exterior to these, formed by the edges of the carapace. Within 

 these were series of punctures, deepest behind, in which the four 

 marks left by the nails of the posterior feet were most prominent, 

 and sometimes the only marks seen. In the centre was an ir- 

 regular groove formed by the tail spine, which was drawn along 



* Limulus poly phemus^ Latreillej Polyphemus occidentalism Lamarck. 



