Chap. X.] 
UPPER S1LUEIAN CORALS. 
217 
indices of the Lower Silurian division. In Bohemia, however, as we learn from 
the work just cited, the foliaceous types are mixed together with the single-sided 
forms (Graptolithi) in the lower part of the upper division. 
The Polyzoa are numerous, but not so numerous in species in the upper as in 
the lower division. Ptilodictya has been already quoted from the Llandovery 
rocks (p. 208). A large species, Pt. lanceolata, Foss. 50. f. 6, is abundant in 
Wenlock strata (f. 7 is its young state) ; and Pt. scalpellum, Foss. 51, accompanies 
Fossils (51). An Upper Silurian Polyzoon. 
Ptilodictya scalpellum, Lonsdale (Eschara, Sil. 
Syst.), natural size. Also a portion magnified. 
It is a common species in the Wenlock limestone, 
and grows larger than represented in the figure. 
it : the former occurs also in the Ludlow rocks. Glauconome disticha, Foss. 50. 
f. 5 ; Fenestella Milleri, f. 4 ; and F. subantiqua, Foss. 30. f. 1, are common fossils 
at Dudley. Another common species, F. assimilis, Foss. 50. f. 2, is also figured, 
as well as the beautiful little cup-shaped Fenestella of the Wenlock limestone, 
F. Lonsdalei, D'Orb., f. 3. Polypora crassa, f. 1, is not so often met with. 
The true Corals (Zoantharia of naturalists) are far more characteristic of the 
upper than of the lower members of the Silurian rocks, and they are more 
abundant in them, both as to species and individuals, — the nodular limestone 
bands of the Wenlock and Aymestry rocks being frequently made up of Corals, 
or of concretions having coralline bodies as their nucleus or on their surfaces. 
When Mr. Lonsdale undertook, at my request, his admirable description of 
the Corals of the Silurian region, and carefully superintended the drawing of 
their forms, sixty-two species only were recognizable in our collections ; and 
these included some of the Polyzoa above mentioned, now known as Mollus- 
coidea, and to be closely allied to the Mollusca. But the number of Corals has 
been greatly increased of late years, chiefly, as regards Britain, by the researches 
of Professors Milne-Edwards and M'Coy. Several new genera have been formed, 
which, as they are founded on peculiarities of structure, growth, and reproduc- 
tion, are likely to prove of permanent value to the zoologist and geologist. 
One of the most important of these discoveries, resulting from the labours of 
Professor Milne-Edwards, and his coadjutor M. Jules Haime*, appears to be, 
that the majority, if not all, of the Corals of the Silurian system, and indeed of 
the whole Palaeozoic era, belong to divisions of the Coral tribe unknown in 
modern seas : with rare exceptions, these groups became extinct at the close of 
the Palaeozoic epoch. If this be established, and the large Cup- and Star-corals 
(Zoantharia rugosa) and the massive Millepores (Z. tabulata) be, as a whole, 
distinct in structure from the Star-corals and Madrepores of the Secondary and 
Tertiary rocks and of the existing Coral-reefs, we gain a new fact in the history 
of animal life upon the globe, which is in harmony with results obtained by the 
study of the Crustacea, Mollusca, and Fish of the older epochs. 
A number of Corals which pass from the Lower to the Upper Silurian rocks 
have already been enumerated (Chap. VI.) ; and as these are generally the most 
abundant species in the younger division, a brief list of them is here given. 
The Chain-coral, Halysites catenularius, Foss. 20. f. 6, p. 120, is one of the 
most frequent ; Favosites Gotlandicus, Foss. 18. f. 2, 3 ; F. alveolaris (F. asper 
of d'Orbigny), f. 4 ; F. (Stenopora) fibrosus, f. 7, 8; Heliolites interstinctus (Po- 
* Archives du Mus. d'Hist. Nat. vol. v. 
