1852.. M'COY SILURIAN FISH AND CRUSTACEANS. 15
shagreen of the same fish, in all probability, of which fragments of
the bony dorsal rays .Onchus tenuistriatus) are so common inter-
mingled in the same mass. M. Agassiz, judging only from the
drawing (figs. 34, 35, 36), supposed these magnified and isolated
specimens to resemble teeth of the general character of Lepidotus ;
but one glance at the specimens would dissipate this notion, when we
find that they are square and not rounded, that they are as small as
grains of fine sand, and occur in such abundance over large patches
of rock as to resemble thick layers of sand. All these points speak
against their being teeth, but are in accordance with the supposition
of their being the earthy grains or shagreen of the skin of large carti-
laginous fishes ; and, finally, having made an examination of trans-
parent sections in a powerful microscope, I found, instead of the close
dentine of the teeth of Lepidotus, only the loose divaricating tubular
structure usually found in such dermal armature as has no grinding
duty to perform.
Postscript. — The specimens forwarded to me, from the Collection
of the Geological Society, as supposed Ichthyodorulites from the
Wenlock limestone of Whitfield, Tortworth, are the nacreous,
shelly tubes of a new species of Serpulites, which I name S. perver-
sus from the singular character of the general curve of the fossil
being in a plane at right angles to that in which the tube is com-
pressed. The average length is 3 inches, and width 2\ lines at the
large end.
Serpulites perversus .M'Coy), from Whitfield Quarry, near Tort-
worth, Gloucestershire. Collected by T. Weaver, Esq., F.G.S.
a. Side view of a large specimen ; natural size.