PACKARD. — RHODE ISLAND CARBONIFEROUS. 403 



passing across the surface. The edge is margined somewhat as in 

 Pandalus. 



I was at a loss to what group to refer these remains, but on showing 

 them to Prof. C. E. Beecher he suggested that they might be crustacean, 

 and I am inclined to agree with him. The sides of the segments of 

 Acanthotelson are no wider ventrally than tergally ; there is also no close 

 resemblance to the segments of Palieocaris, both being from the Carboni- 

 ferous beds of Mazon Creek, Illinois. It is possible that they may be- 

 long to some true shrimp such as Anthrapala^mon or other macrurau of 

 that period. 



Ostrakichnites carbojiarius {Protichnites carbonarius) Dawson, Acadian Geology 3d 

 edit., 1878, p. 55. Fig. 9, a. 



Dawson describes and figures certain tracks from the millstone grit 

 formation at McKay's Head in No^a Scotia which he refers to 

 Protichnites and whicli he supposes to have been made by a Limulus- 

 like animal. 



Somewhat similar but much less regularly arranged tracks occurred in 

 a boulder of fine red shale found in a stone wall at South Attleboro, kindly 

 given me by Mr. J. H. Clarke. The tracks were associated with mud 

 cracks, raindrops, and the worm-like impression already mentioned. 



They are of the same size as those figured by Dawson, but are not so 

 regularly arranged, being much more scattered, and with no median 

 linear tail-mark. Yet the individual impressions are of the same shape and 

 size, and so like those of Dawson's Protichnites that they were apparently 

 made by the same kind of animal and could perhaps have been made 

 by the e.xtremities of the feet of a small shrimp-like creature. 



The impressions are in sets of three, each of which is round in front, 

 deep and succeeded behind by a shallow faint furrow, showing where the 

 tip of the foot or spine of the hinder feet had trailed over the mud, 

 before the final impress of the feet was made. The three impressions 

 are not arranged in a straight line, but in a slightly curved line, showing 

 that the middle spine or claw was longer than the lateral ones. In some 

 cases there are single impressions forming two series about 8 mm. apart, 

 but with no tail-mark between. 



The Protichnites tracks figured by Dawson, could not have been made 

 by a full grown Euproops or Prestwichia, and it should be observed that 

 the set of three prints is quite different from the long oblique crescentic 

 tracks made by the hind cephalic legs of Limulus. The tracks might as 

 well have been made by the crustaceans Gampsoiiychus, Anthrapaleemon, 



