484 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 11, 
3. Are Protichnites and Climactichnites the tracks of Trilobites? 
In his description of Protichnites, Pref. Owen says :—‘“ The 
Limulus, which has the small anterior pair of limbs (near the 
middle line) and the next four lateral pairs of limbs biturcate 
at the free extremity, the last pair of lateral limbs with four 
lamelliform appendages, and a long slender hard tail, comes the 
nearest to my idea of the kind of animal which has left the impres- 
sions on the Potsdam sandstone’*. In 1862, Dr. J. W. Dawson 
tested this opinion by actual experiment, on a sandy beach near the 
mouth of the Scarborough river, on the coast of Maine. Having 
caught a Limulus he kept it alive for several days, and “ tried its 
mode of locomotion under various conditions on the sandy shore, and 
preserved sketches of the markings”f. His figures and descriptions 
prove clearly that the tracks on the sandstone could have been made 
by an animal having a structure like that of Limulus. The grooves 
along the side of the track were made by the edges of the broad 
cephalothorax, the small pit-like impressions by the extremities 
of the large limbs, the transverse grooves by the lamelliform feet, 
and the median groove by the telson. Ifit be granted that Asaphus, 
in addition to its thoracic legs, possessed a set of lamellar swimming- 
appendages under the pygidium, then the structure of the under- 
surface would be sufficiently hike that of Limulus to enable it to 
produce the same markings. The median groove might be made by 
a Trilobite with a caudal spine like that of Megalaspis heros (Angelin). 
This species 1s a true Asaphus. The large Trilobite of the Potsdam 
sandstone, Dzkelocephalus, differs little in general structure from 
Asaphus, while the pygidium of several of the species evinces a ten- 
dency to become spinous around the margin. The genus Aglaspis 
(iiall) appears to me to be a Trilobite of the same group; and, more- 
over, the specimens figured scem to be the tail and not the head. 
What are supposed to be the eyes are the bases of two spines, lke 
the one that occurs on the pygidium of Bathyurus spiniger (Acidas- 
pis spinger, Hall). 
Dr. Dawson, after comparing all the facts, says :—‘‘ On the whole 
we may safely conclude that, if any of the larger primordial Trilobites 
were provided with walking- and swimming-feet of the type of 
those of Limulus, but differing in details of structure, they may have 
produced both the Protichnites and the Climactichnites.” Prof. 
J. D. Dana, also speaking of the latter, says:—‘It has been re- 
garded as the track of a very large Gasteropod; but it is quite as 
probable that it was made by the clusters of foliaceous appendages 
of one of the great Trilobites—these appendages being its locomotive 
organs”, The following, thercfore is the present state cf the ques- 
tion :— 
1. The tracks could have been made either by a Limulus or by a 
Trilobite. 
* Quart. Journ. Geol. Soe. vol. viii. p. 224. 
t Canadian Naturalist and Geologist, vol. vil. p. 276. 
{ Manual of Geology, p. 185. 
