188 
SILUKIA. 
[Chap. IX. 
view of their Sertularian affinities ; but that they were Polyzoa some think the 
more certain on account of the discovery of a form intermediate between them 
and the Fenestellse. 
This is the Dictyonema (or Phyllograpsus, as it has been called by Prof. An- 
gelin), which, as already noticed, p. 45, occurs in the Lingula-flags of Wales 
and Shropshire. It combines with the shape and general characters of the net- 
like Polyzoa, the texture and the form of the cells of the Graptolite, and may be 
regarded as a bundle of these animals united by processes into a reticulated cup. 
The curiously complex branched forms of Graptolites discovered by Sir 
W. E. Logan in Canada seem to complete the chain of affinities between the 
Graptolites and the Fenestellidce. 
Besides these inhabitants of ancient muddy seas, which are, as before said, 
exclusively Silurian in all quarters of the globe, many forms of true Polyzoa are 
seen even ".in the lower portion of these deposits, and are abundant through- 
out the series. These were formerly confounded with Corals, and in the eye 
of the field-geologist might still pass for such, though they are really low forms 
of Mollusks, having even no distant affinities with the Brachiopoda ! They are 
here associated in the same woodcuts (Foss. 30 & 31) with the Corals. 
Fossils (30). Lower Silurian Zoophytes and Polyzoa. 
1. Fenestella subantiqua, 
d'Orbigny. 
2. Ptilodictya acuta, Hall. 
3. Mdulites favus, Salter*. 
4. Sarcinula( Syringophyl- 
lurn, Milne-Edw. and Haime) 
organum, Linn. 
5. Heliolites inordinatus, 
Lonsdale. 
6. Favosites Gotlandicus, 
Goldfuss. 
7. Heliolites megastoma, 
M'Coy; a species with large 
cells, found in Pembroke- 
shire. 
The species with a net-like form, Fenestella and Retepora, though occa- 
sionally met with in Caradoc rocks, are not common as Lower Silurian 
forms. The most frequent are flat-branched forms allied to the living Eschara 
of our coasts, and which are known by the name Ptilodictya, Lonsdale (Escha- 
ropora, Hall). Pt. acuta, Foss. 30. f. 2, and Pt. dichotoma, Foss. 31. f. 5, 
are common species, and occur low down in the series. The more expanded 
forms, Pt. explanata, M'Coy, and Pt. fucoides, M'Coy, are found rather in the 
upper portions of the true Caradoc strata in Wales. Here, too (if not in a still 
higher series, or at the base of the Llandovery rocks), Fenestella subantiqua, 
d'Orb. (F. antiqua, Sil. Syst.), Foss. 30. f. 1, makes its appearance. There are 
also some other forms, both branched and encrusting, which occur in the higher 
Caradoc strata of Wales. Glauconome disticha, Foss. 50. f. 5, and Fenestella 
Milleri, f. 4, are found both in the Wenlock beds and in the Lower Silurian cal- 
careous slates of Llansaintftraid, Glyn Ceiriog, in Denbighshire. 
Of the Corals, the most prevalent are certain species of the genera Halysites, 
Heliolites, Favosites, and Petraia. 
One of the most striking of these bodies, which ranges into and abounds in 
the Upper Silurian, and is widely spread through various countries, is the Haly- 
* This curious fossil belongs truly to the Llandovery rocks, and will be noticed when their fossils 
are described. It is doubtfully referred the Polyzoa. It is not a Coral. 
