xvi DESCRIPTIVE REMARKS. 
ferous limestone—but does not, in our opinion, present any special charac- 
ters connecting it so much with the Graptolites as Mr. Salter considers 
it to do: the projecting corneous cells, alluded to by him as a distinc- 
tive character,* are quite as evident in some species of Fenestella, re- 
sembling very closely F. frutex, M‘Coy. The Fossils called Callograptus 
and Dendrograptus by Professor Hall appear to exhibit more closely an 
intermediate stage, and to connect these net-like forms with the branch- 
ing Graptolites. It is of considerable interest, however, as the oldest 
known form of Polyzoa in British strata, and as characterizing the 
‘Primordial Zone’ of Barrande; the equivalent of the Lingula Flags 
of Britain.t+ 
The Brachiopod shell, Lingulella Davisit, Plate iii., fig. 3 (formerly 
called Lingula), said to be the commonest of all the Lingula Flag Fossils, 
belongs to a family of which the following genera are represented in 
British Silurian Rocks, viz., Lingula, Lingulella, Obolus, and Obo- 
lella.t 
It is widely distributed, and very abundant throughout the Trema- 
doc district of North Wales, some of the slaty beds being full of these 
shells, in which, however, their true shape is rarely preserved, being 
more or less flattened and distorted; it has been also found near St. 
David’s Head, Pembrokeshire. 
The small Orthis lenticularis, Plate iii., fig. iv., the earliest known in 
British rocks (believed by Mr. Salter to be identical with a Swedish 
species), is found in the Upper Lingula Flags, near Tremadoc ; the Welsh 
specimens are described as occurring in myriads in some of the shales. 
The Crustacea of the Lingula Flags, with one exception, are all 
Trilobites, that of Hymenocaris vermicauda, Plate iv., fig. 1, described 
as belonging to the Phyllopoda, and said to be abundant in the fine 
slaty layers at the upper part of the Lower Lingula Flags, near Port- 
madoc, in North Wales. The lowest and most rudimentary form of 
Trilobite, Agnostus, furnishes a species—A. princeps, fig. 2—met with 
in the greatest profusion in some of the beds of the Lower Lingula Slates, 
associated with others of a higher character. 
The remarkable Trilobite Paradoxides Davidis, fig. 3, the largest of 
all British species, first discovered by Mr. Salter at St. David’s Head, 
Pembrokeshire, South Wales, is also included by him amongst the 
Fossils of the Lower Lingula Flags, as occurring at Dolgelly, North 
Wales.§ 
The gems Olenus, which includes Paradowides, is the most charac- 
teristic and abundant of all the Trilobites of the Lingula Flags. We 
* Memoirs of the Geological Survey, vol. iii., p. 332. 
+ Siluria, third edition, p. 562. 
{£ The genus Lingula ranges from the oldest strata up to the present time; as a re- 
cent genus, it is few in number of species. Mr. Davidson enumerates fifteen fossil 
species of British Silurian Lingule, and ten additional, not yet sufficiently made out, 
several of which, when better known, may prove to be synonyms. British Silurian 
Brachiopoda, pp. 33, 34. 
§ Memoirs of the Geological Survey, vol. iii., pp. 247, 248, and Decade xi., De- 
scription to Plate x., p. 4. 
