PLATE 127, 28. 
fresh water horse muscle. His supposition respecting the 
recent shell was correct, if by the horse muscle he meant the 
Mya ovalis, a common species in our rivers, and most un- 
doubtedly the original of the present fossil. The shells, 
however, generally called horse muscles (Mytilus cygneus. 
& Myt. anatinus) which are still more common than the 
Mya ovalis, and frequently found with it in the reeent state, 
I have not, as yet, observed in any of the ironstones of 
Derbyshire. It is probable, they may occasionally occur, 
with other fresh water shells*; but the principal mass of 
organic remains, forming the white figures in the stone 
when broken, (see fig. 5) and of which, indeed, the stra- 
tum almost wholly consists, will be found, on a careful 
comparison of the fossil with the recent species, to have 
originated from the Mya in question. 
Fro. 1. A specimen of one of the shells in the most per- 
fect form they are ever procured, from the surrounding 
stone. 
2. The same, in a different position — showing the beaks 
and back of the hinge. This specimen is wholly ironstone : 
* I have been informed, that a species of ^viinonites has been found irj 
the solid stratum of ironstone, as well as in nodules, near Wingerworth. I 
have not seen the specimens ; but, as the Ammonita, and every kind of 
fossil Nautili yet known, are certainly marine productions, it is probable, 
the shells taken for such, will prove to be the remains of the Helix cornea, 
or of some other species of the depressed univalves, which inhabit our still 
rivers and pools ; for it rarely happens, that the productions of the sea are 
mixed, in the fossil state, with those of the land, or fresh water. 
