102 C. U. Shepard on supposed Tadpole impressions 
bevelled; and in one case for a little distance, I have seen them 
replaced by four narrow planes. But the most singular feature 
of those specimens with a single broad band, consists in the 
as it were to the scar on the contiguous band. 
It should further be mentioned that the repetitions of these im- 
pressions of each separate sort are very numerous, and eac 
the imprints may have owed their origin to a gigantic species of 
alga, allied to the Hydrodictyon utriculatum, though constituting 
a different genus, and possibly pertaining to a different family 
‘ 
