66 PROCEEDINGS OF THE AMERICAN ACADEMY. 



sembling ripple marks (Fig. 3). These were produced by the sand 

 swept up by the swimming feet." Dr. Dawson then compares the trail 

 represented by his Fig. 3 with Logan's Climactichnites, and they are 

 remarkably similar, except that the oblique furrows made by the legs 

 between the median and lateral ridges are directed in the reverse 

 direction. 



Of the tracks afterwards described and figured by Dr. Dawson * from 

 the upper Carboniferous of Nova Scotia, none seem to me to be referrible 

 to trilobitic or merostomatous trails. Protichnites carbonarius, as already 

 remarked in these Proceedings, f appear to have been made by a crusta- 

 cean, and we have referred them to a distinct genus, Ostrahiclmites. 



Some years ago I made some experiments with small Limuli by placing 

 one in a shallow tin pan, in which the sand was about half an inch deep, 

 and the water not deep enough to entirely cover the body. The animal, 

 so far as I can now remember, used its ambulatory feet in walking, while 

 the swimming or abdominal legs were partially used. The result may 

 be seen in Fig. 1. The king-crab was about four inches (10 cm.) in 

 width. The trail it made consisted, besides the tracks themselves, of an 

 outer ridge made by the outer edge of the head or carapace ; this ridge (d) 

 was about 15 mm. in width, and was due to the heaping up of the fine 

 sand ; in section it would be low conical ; one would suppose that the 

 action of the edofe of the head would make a furrow rather than an ele- 

 vated ridge. 



The tracks (t) were opposite, and quite regularly concavo-triangular, 

 the apex of the triangle rounded, and directed backwards, the sand being 

 pushed slightly up on the jDOSterior edge of the track. 



The tracks of each side were directly opposite each other, and those of 

 each pair directly in line with those of the pair in front. It was noticed 

 that the distance apart of the tracks varied with the rapidity of the half- 

 walking, half-swimming movements of the animal. It was seen that the 

 tracks were made by the hindermost, or sixth pair, of limbs only, no im- 

 pression being left in the sand by the feet in front. The triangular 

 shape of the track was due to the spreading out of the two spatulate 

 spines of the last segment of the leg. It should be observed that the 

 distance apart, outside measurement, of the tracks is about two-thirds 

 that of the entire trail. 



* Impressions and footprints of aquatic animals and imitative markings on 

 carboniferous rocks. Amer. Journ. Sc. and Arts, 3d Series, V. Jan. 1873, pp. 16-24, 

 Figs. 1-5. Also Acadian Geology, 2d edit. Supplement. 1878. 



t XXXV. AprU, 1900, p. 403. 



