196 



ON SOME TRAILS AND HOLES FOUND IN EOCKS 



and indeed in all other beds of shells which have been gene- 

 rally classed under the genus unio, it has been found. Most 

 of the black shales forming the roofs of the coals in the mid- 

 dle and upper coal fields, and the limestones of Ardwick, 

 yield it. But, with the exception of Shaly Brow, it is the 

 most plentiful in the roofs of the yard and three-quarter 

 mines of Bradford near Manchester, mingled with a mass of 

 cypriS) and detached bones, scales, and teeth of fishes. 



The genus microconchus probably had better for the 

 present be divided into two genera, namely, spirorbis and 

 serpula; under spirorbis, I propose to class, — 



1st. The small one figured by Sir R. Murchison, found in 

 the shales and limestones of Ardwick. This is sometimes 

 attached to plants and shells found in the shales, and has evi- 

 dently lived as a parasite both on floating plants and shells, 

 lying at the bottom of the waters just as the common spirorbis 

 now found on our shores does. The specimen described in 

 plate II. fig. 3, is one-twentieth of an inch in diameter, and 

 was found by me on a fossil bivalve shell from the roof of the 

 Four Feet Mine at Bradford near Manchester. I propose to 

 call it spirorbis carbonarius. 



2nd. S. omphaloides, of Goldfuss and Portlock. A large 

 species, found in many places, especially amongst the bed of 

 large bivalve shells lying above the Arley Mine at Wigan, 

 and other places, and the shales of Shaly Brow. This species 

 apppears to be identical with the one found by Martin, near 

 Chesterfield, and figured by him under the name of conchy- 

 liolithus heliciles. The specimen described in plate II. fig. 4, 

 is two-tenths of an inch in diameter, and was found by me in 

 the roof of the lower seam of coal in Mr. Stock's colliery at 

 Shaly Brow. 



The large uncoiled shell appears to me more properly 

 arranged under serpula. It is by no means so common as the 

 two species of spirorbis previously described, and I have not 

 yet found it attached to fossil plants or shells like those, but 



