18 J. W. Dawson—Footprints, ete., on Carboniferous Rocks. 
pressure of a pair of flat organs, crenated or toothed at the 
edges, rather than divided into separate toes. Its horizon is 
the Lower Carboniferous. It was collected by Prof. Hartt. 
he first species of Protichnites referred to above may be 
appropriately named P. Carbonarius, and the second P. Acadicus. 
They are, I believe, the first impressions of this kind found in 
the Carboniferous. 
2. Rusichniies Dawson. 
In a paper published in the Canadian Naturalist, 1864, I 
showed that the singular bilobate markings with transverse 
strie named Rusophycus by Hall, and found in the Chazy of 
Canada and the Clinton group of New York, are really casts of 
burrows connected with footprints consisting of a double series 
of transverse markings, and that a comparison of them with 
the trails and burrows of Limulus justified the conclusion that 
itthey were produced by Trilobites. I proposed for these and 
for similar impressions of small size found in the Carboniferous, 
the name given above. The Carboniferous examples I supposed 
might have been produced by the species of Phillipsia found in 
these beds. specimen recently obtained from Horton shows 
this kind of impression passing in places into a kind of Pro- 
tichnites, as if the creature possessed walking feet as well as the 
lamellate swimming feet which it ordinarily used. 
I can scarcely doubt that the Cruziana semiplicata of Salter, 
and C. similis of Billings from the Primordial of Newfound- 
land, must have been produced by crustaceans not dissimilar 
from those to which Rusichnites belongs. 
To Rusichnites rather than to Protichnites ought perhaps to 
‘be referred certain transverse linear impressions with a broad 
-eentral groove from the Lower Carboniferous of Horton, which 
‘occur at that place under different modifications, and sometimes 
‘seem to change into light scratches or touches of feet employed 
in swimming, or end abruptly as if the animal had suddenly 
risen from the bottom. 
Arenicolites Salter. 
This genus may be held to include cylindrical burrows of 
worms with or without marks of minute sete. They occur in 
rocks of all ages, and are especially abundant in the Lower 
Carboniferous series of Half-way River, Nova Scotia, and in the 
Upper Coal-formation at Tatamagouche in the same province; 
those at the latter place showing minute scratches produced by 
the setee of the worms.* With the ordinary form at Horton 
there occur very long and slender, thread-like forms of the same 
nature with those to which the name Nemertites has been given. 
* Journal of the Geological Society, vol. ii. 
