88 PROCEEDINGS OF THE AMERICAN ACADEMY 



ladder-like rows, of which the specimen shown contained several, we 

 should hardly doubt that they are tracks ; but the whole slab is cov- 

 ered with analogous markings, and there are some rows of them that 

 seem as if of vegetable origin. Though a name is for convenience 

 attached to these specimens, yet it is extremely difficult to make up 

 one's mind as to their character. 



19. Perhaps Crustacean Tracks. 



Some large and remarkable slabs were described under this head. 

 On these slabs, the largest three and a half by four and a half feet, 

 may be noticed the following : — 



1. Several perfectly straight grooves or furrows, perfectly parallel, 

 sometimes not half an inch apart, resembling drift furrows. 



2. Numerous rows of impressions, not less certainly than thirty-five, 

 running across the slab, nearly parallel to one another and to the 

 grooves, but sometimes intersecting at a small angle, and apparently 

 independent of the grooves. 



3. Circular dents, as if made by a blunt stick, but nearly equidis- 

 tant ; sometimes elongated and linear, sometimes boot-shaped, some- 

 times with a trifid arrangement in equidistant steps. 



4. Three deeper and distinct furrows, parallel to the others, evi- 

 dently tail-traces, from which small ripple-marks proceed like the 

 vane of a feather. 



An excellent photograph of the largest slab was exhibited ; also 

 outlines, several inches long, of the ten or twelve varieties of impres- 

 sions of the natural size. By the aid derived from a recent paper in 

 the Canadian Naturalist, by Dr. Dawson, " On the Footprints of Limu- 

 lus, as compared with the Prototichnites of the Potsdam Sandstone," 

 the suggestion was made that these impressions might have been the 

 work of an analogous Crustacean. 



Supposed Mistake as to the member of Phalanges in the thick-toed 

 Animals that made the Footmarks in the Connecticut Valley. 



The opinion seems to have been unanimous, with all who have 

 examined the footmarks of the Connecticut Valley, that the number 

 of phalanges denoted by the impressions in the thick-toed bipeds 

 corresponds to those of most tridactyle birds, viz. (omitting the ungual 

 phalanx, which would not show an impression distinct from that 

 made by the penultimate phalanx) two in the inner toe, three in the 

 middle, and four in the outer toe. And this is certainly the con- 



