DESCRIPTIVE REMARKS. xX1x 
fig. 4, and Nebulipora favosa, fig. 2, are Zoophytes or Corals, the two 
former considered to belong to the Gorgonide, the latter to the Favosi- 
tide, a group of the division Zoantharia tabulata of Professor Milne 
Edwards; it resembles very closely some of the varieties of Stenopora 
(Favosites), fibrosa, small Corals, generally branching, and composed 
of an aggregation of basaltiform corallites belonging to the same family ; 
first appearing in this Formation, and continuing throughout the re- 
mainder of the Silurian rocks, but most abundant and characteristic of 
the next or superimposed Formation, that of the Caradoc or Bala, with 
the Fossils of which we have figured it, Plate x., fig. 1. 
It is not until we reach the Upper Silurian that we meet with many 
of the larger kinds of Corals, those which secrete a calcareous frame- 
work, and are in consequence so easily preserved as Fossils; they are 
abundant in the Wenlock limestone. There may have been, however, 
during the period of these earlier deposits, softer kinds, such as the 
Actinie (Sea Anemones), and allied forms, which would have been un- 
preservable, and of which, therefore, no traces remain. 
The portion of an Encrinite stem, fig. 5, referred to Cyathocrinus 
by Mr. Salter, is stated by him to be the earliest British record of the 
order Crinoidea, which afterwards became so abundant throughout the 
Paleozoic strata. 
The singular markings called Nereites Cambrensis, fig. 6, with 
others of a somewhat corresponding character, have been usually de- 
scribed, from their resemblance to marine worms, as Annelidan ; but, as 
we are now aware that some of the shell-bearing, as well as soft Mol- 
lusca, and other marine animals, during their locomotion produce sinu- 
ous tracks over the smooth surface of sand, as well as burrow through 
it, and even excavate cavities in the hard rock, it would not be safe to 
rely too confidently on such markings as exact evidences of the class to 
which they have been referred ; they are nevertheless useful as charac- 
terizing particular sandy and flaggy beds, in this and more recent For- 
mations in which there are often no other remains perceptible. We 
have in figures 7 and 8 more tangible evidence of the Annelida. Fig. 
7 is referred by Mr. Salter to Arenicolites, fig. 8 to Scolites: the latter 
he believes to be the ordinary fillings up of worm tracks in the sandy 
mud, and for such he proposes to retain the name of Scolites; for those 
which show double vertical burrows, such as fig. 7, that of Arenicolites. 
The Trilobites figured on Plate vii. consist of examples of those 
genera which are most frequent, as well as characteristic of this Forma- 
tion; a small species of Agnostus, named A. MU Coyzi, fig. 1, belonging 
to a genus before alluded to (ante, p. xvi.), as being the most rudimentary 
form of the group ; and, on the contrary, one of the largest and well de- 
veloped of these Crustacea is that of Asaphus tyrannus, of which fig. 2 is 
a reduction ; it is said to be eminently characteristic of the Upper Llan- 
deilo, not ranging above that Formation, and limited to the British area. 
Ogygia Buchit, fig. 8, is another very important Trilobite, particularly 
abundant in the Llandeilo shales, near Builth, and believed to be also 
confined to the same Formation. A small Trilobite, Zglina binodosa, 
