70 PROCEEDINGS OF THE AMERICAN ACADEMY. 



its elliptical body. The trail seems to indicate the occurrence of a mero- 

 stome of a group not represented by any known fossil genus, unless it 

 Bhould prove to be a young Protolimulus. 



Merostomichnitei narragansettensis (Pack.). Fig. 5. Proc. Araer. 

 A i. Arts and Sci. XXXV. No. 20, April. 1900, p. 402. Three 

 trails of this species were discovered by a member of my geological class, 

 — Mr. II. II. Mason, of the class of 1900, — and kindly given to me, while 

 doing field work under my direction in Providence, R. I., just north of 

 the city and of the North Burying Ground. The trails occurred in a 

 rounded pebble of dark arenaceous shale picked up from the mass of 

 water-worn gravel and boulders constituting the body of a large rounded 

 kame. It was split in two, so as to show the impressions and the relief 

 of the tracks. The subglacial deposits at this point are derived from a 

 region a few miles a little east of north, probably in the vicinity of South 

 Attleboro, though I have not seen beds of this peculiar blackish sandy 

 shale in place. 



There are three trails, — one separate, and the two others crossing 

 each other. The long separate series is nearly straight, 6.50 cm. in 

 length ; the other trail is sinuous, and is crossed by a third, shorter trail. 

 The width of each trail is the same, being about 12 mm. outside meas- 

 urement. The distance between the individual tracks of the same pair 

 is about 9 mm., that between the footprints on the same side varies from 

 about 2 mm. to about 4 mm. 



The tracks are opposite and not alternate. Along most of the length 

 of the trail there is but a single series of tracks on a side, but in portions 

 of the entire trail the footprints are double, there being an inner and an 

 outer set on each side. If we select four of the tracks in a place where 

 they are double, it will be seen thai they are arranged in a very low trap- 

 ezoid ; while the Bpace between the two outside tracks is 9 nun., that 

 between the two inner, a little in advance, is o nun. 



The individual tracks forming the trails are of quite uniform shape, the 

 best marked ones being transversely oval or crescentie in outline, the 

 mud having been pushed back by the animal's feet so as to leave a cres- 

 centie ridge, the concavity pointing forward. The m/.c .it' the impression 

 in tran diameter is about 3 mm., the longitudinal diameter L.5, 



i. e. the tracks are about twice as broad as long. Tims they are not 

 linear, and more or less parallel to the main series of tracks, as in those 



referred to the decapod Crustacea. In two or three cases the tracks are 



Connected by B slight ridge curved forward in the direction the animal 



mo\ ed. 



