In the same grey paving-stones and coarse roofing-slates, in which the Cephalaspis occurs, in Forfarshire and Kincardineshire, the remains of marine plants or fucoids abound. They are frequently accompanied by groups of hexagonal, or nearly hexagonal markings, which consist of small flattened carbonaceous bodies, placed in a slight depression of the sandstone or shale. (See [figs. 397] and [398.]) They much resemble in form the spawn of the recent Natica (see [fig. 399.]), in which the eggs are arranged in a thin layer of sand, and seem to have acquired a polygonal form by pressing against each other. The substance of the egg, if fossilized, might give rise to small pellicles of carbonaceous matter.
Fig. 399.
Fragment of spawn of British species of Natica.
These fossils I have met with, both to the north of Strathmore, in the vertical shale beneath the conglomerate, and in the same beds in the Sidlaw hills, at all the points where [fig. 4.] is introduced in the section, [p. 48.]
Fig. 400.
Pterichthys, Agassiz; upper side, showing mouth; as restored by H. Miller.[345-A]