J. W. Dawson—Footprints, etc., on Carboniferous Rocks. 17 
shown by me in 1862* to correspond precisely with those of 
the American Limulus (Pelyphemus occidentalis). I proved by 
experiment with the modern animal that the recurring series of 
groups of markings were produced by the toes of the large 
posterior thoracic feet, the irregular scratches seen in Protichnites 
lineatus by the ordinary feet, and the central furrow by the tail. 
It was also shown that when the Limulus uses its swimming feet 
it produces impressions of the character of those named Climac- 
tichnites, from the same beds which afford Protichnites. The 
principal difference between Protichnites and their modern 
representatives is that the latter have two lateral furrows pro- 
duced by the sides of the carapace, which are wanting in the 
former. : 
As Limuloid crustaceans are well known in the Carbonif- 
erous beds of Europe and America, their footprints might be 
expected to occur in rocks of this age, but the first I have met 
with were sent to me last summer by my friend Mr. Elder, of 
Harvard College, who found them quite abundantly in dark- 
colored flag-stones belonging to the Millstone Grit formation at 
McKay’s Head in Nova Scotia (fig. 1). The animal which pro- 
duced these marks must have been of small size (about half an 
inch in breadth), in this agreeing with the usual size of the 
Coal-formation Limuloids; and like the ancient Protichnite- 
makers, it left no trace of the edges of the carapace, but a very 
distinct impression of a sharp pointed tail. Its posterior feet 
had three or possibly four sharp toes. There were besides 
several pairs of sharp-pointed walking feet. On the same slabs. 
there are some series of marks, evidently made by the same 
kind of animal, which have no tail-mar , and there are tail- 
marks with only traces of those of the toes. It is worthy of 
notice that, though these tracks indicate the presence of the ani- 
mals, no crusts of Carboniferous Limuloid crustaceans have yet 
been found in Nova Scotia. The sand in which the tracks now 
referred to were made was probably too hard to permit the 
swimming feet to make any impression. With respect to the 
absence of the marks of the sides of the carapace, I may ob- 
Serve that the genus Belinurus of the Carboniferous had the 
sides of the carapace less deep than that of the modern Limu- 
lus, and this may also have been the case with the more ancient 
Limuloids of the Potsdam. See as to this a letter by Prof. Hall 
In = waite Naturalist, Be Wa ‘natensedl a veep ohare 
0 Protichni a e reife a § : 
i Hive aig Phas bia (Gs , which at first sight much 
resembles P. Scoticus, from the Primordial of Roxburghshire, 
* Canadian Nat., vol. vii. ' + Siluria, 4th edition, p. 153. 
Am. Jour. Sct.—Tuirp Series, Vor. V, No. 25.—Jan., 1878. 
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