DESCRIPTIVE REMARKS. XV 
lations of members of the series; all the modifications of which have 
been recognised in the last edition of Siluria.’’* 
Although the remains of organic life exhibit but little increase 
in the lower divisions of strata, immediately superimposed upon the 
Cambrian, yet there is a marked difference in their character, and they 
become much more evident as to their relations in the animal series; 
rapidly adding to their numbers and variety of forms towards the upper 
portion of the series; the following classes, all confined to the Inverte- 
brata being represented :— 
Zoophyta, or Corals, few; Mollusca, especially Brachiopod shells, 
abundant ; of the Zchinodermata, Crinoids few, Cystidea more numerous; 
Annelida few ; and of Crustacea, the extinct group of Trilobites abun- 
dant. 
Fosstis oF THE Lincuta Bens. 
The designation ‘‘ Lingula Flags’ was first applied to those rocks, 
by Professor Sedgwick, in consequence of the discovery by Mr. Davis 
in rocks near Tremadoc, in 1845, of the shell named after him Lingula 
Dawvisvi (since called Lingulella by Mr. Salter), which was found to be 
so characteristic and abundant as to give the name to the formation. 
These beds, divided into upper and lower by the Geological Survey, oc- 
cur in North and South Wales, above the Cambrian Grits, near Bangor; 
near Bala, in Merionethshire ; and at St. David’s Head, Pembrokeshire ; 
also in Shropshire ; the series of strata occurring there being described 
by Sir R. Murchison, as ‘a great mass of dark coloured schistose shale, or 
consolidated mud, reposing upon the Cambrian Rocks of the Longmynd 
Mountains ;” and, as forming the base of his system, since observed to be 
the equivalents in position of the Welsh Lingula Flags, although not 
yet found to contain Fossils.t| At Malvern, black shales with Trilobites, 
first described by Professor John Phillips,t are also believed to belong 
to the same series. 
On Plates iii. and iv. are figured the principal Fossils from these beds. 
They consist of what is supposed to be worm tubes or burrows (Azmneli- 
dan?) named Cruziana semiplicata, Plate iii., fig. 1, and Chondrites, oc- 
curring, as Mr. Salter informs us, in matted masses, on the largely ex- 
posed surfaces of the arenaceous flags; the remarkable net-like Fossil, 
Dictyonema sociale, Plate iii., fig. 2, described by him as a Bryozoan or 
Polyzoan, and as forming a connecting link between the Graptolites and 
Fenestellide ; abundant in the uppermost Lingula Flags near Trema- 
doc, and very generally distributed ; occurring also in Shropshire and 
the Malverns. This fossil (identified by the author) has been also col- 
lected by the Geological Survey in Ireland. It certainly appears to be 
intimately related to Fenestella—a genus so prevalent in the Carboni- 
* Memoirs Geological Survey, vol. iii., p. 1. 
+ Introduction to British Silurian Brachiopoda, Pal. Soc., 1866. 
t Memoirs of the Geological Survey, vol. ii., parti., p. 54. 
