The commonest, and at the same time the largest, of these are the “honeycomb corals,” forming the genus Favosites (figs. 84, 85), which derive both their vernacular and their technical names from their great likeness to masses of petrified honeycomb.  The most abundant species are Favosites Gothlandica and F.  Hemispherica, both here figured, which form masses sometimes not less than two or three feet in diameter.  Whilst Favosites has acquired a popular name by its honey-combed appearance, the resemblance of Michelinia to a fossilised wasp’s nest with the comb exposed is hardly less striking, and has earned for it a similar recognition from the non-scientific public.  In addition to these, there are numerous branching or plant-like Tabulate Corals, often of the most graceful form, which are distinctive of the Devonian in all parts of the world.

The Echinoderms of the Devonian period call for little special notice.  Many of the Devonian limestones are “crinoidal;” and the Crinoids are the most abundant and widely-distributed representatives of their class in the deposits of this period.

The Cystideans, with doubtful exceptions, have not been recognised in the Devonian; and their place is taken by the allied group of the “Pentremites,” which will be further spoken of as occurring in the Carboniferous rocks.  On the other hand, the Star-fishes, Brittle-stars, and Sea-urchins are all continued by types more or less closely allied to those of the preceding Upper Silurian.

Of the remains of Ringed-worms (Annelides), the most numerous and the most interesting are the calcareous envelopes of some small tube-inhabiting species.  No one who has visited the seaside can have failed to notice the little spiral tubes of the existing Spirorbis growing attached to shells, or covering the fronds of the commoner Sea weeds (especially Fucus serratus).  These tubes are inhabited by a small Annelide, and structures of a similar character occur not uncommonly from the Upper Silurian upwards.  In the Devonian rocks, Spirorbis is an extremely common fossil, growing in hundreds attached to the outer surface of corals and shells, and appearing in many specific forms (figs. 86 and 87); but almost all the known examples are of small size, and are liable to escape a cursory examination.

[Illustration:  Fig. 87.—­a, Spirobois omphalodes, natural size and enlarged.  Devonian, Europe and America; b, Spirorbis Arkonensis, of the natural size and enlarged; c, The same, with the tube twisted in the reverse direction.  Devonian, America.  (Onginal.)]

[Illustration:  Fig. 88. a b, Spirorbis laxus, enlarged, Upper Silurian, America; c, Spirorbis spinulifera, of the natural size and enlarged, Devonian, Canada. (After Hall and the Author.)]

[Illustration:  Fig. 88.—­Devonian Trilobites; a, Phacops latifrons, Devonian of Britain, the Continent of Europe, and South America; b, Homalonotus armatus, Europe; c, Phacops (Trimerocephalus) loevis, Europe; d, Head-shield of Phacops (Portlockia) granulatus, Europe. (After Salter and Burmeister.)]