194 SILURIA. [Chap. IX. 
ferred to the genus Strophomena) extends upwards throughout the whole series, * 
from the oldest Llandeilo beds to the Upper Ludlow rock. 
Of the two species of Leptaena which are prevalent in the lower division, the 
most frequent is L. sericea, PI. V. f. 14, and Foss. 36. f. 6, which, occurring in 
swarms among the slates of Snowdon, is also most abundant and characteristic 
in the Caradoc Sandstone of Shropshire ; whilst L. transversalis, PL XX. f. 17, 
published originally as a fossil of the "Wenlock Shale, is now also found in the 
Caradoc formation of Wales and Westmoreland. The former of the two last- 
mentioned species has indeed a universal range, being known in Russia, Scan- 
dinavia, Central Germany, the British Isles, and America. Leptaena tenuicincta, 
Foss. 37. f. 4, and L. quinquecostata, f. 3, are not unfrequent Caradoc species 
both in England and Ireland : the latter is found deep down in the Llandeilo 
flags. 
Fossils (37). Lower Silurian Brachiopods. 
1. Orthis biforata, 
Schlotheim (internal 
cast). 2. Orthis 
spiriferoides, M'Coy. 
3. Leptaena quinque- 
The Orbiculoid and Cranioid groups, though not common in the lower division, 
yet afford some characteristic species. The remarkable Crania divaricata, Foss. 
38. f. 2, like its congener the Crania antiquissima (Pander) of Russia, is a Lower 
Silurian species. Discina (Treniatis) punctata of the Caradoc Sandstone, Foss. 38. 
f. 1, can with difficulty be distinguished from the beautiful Discina (Treniatis) can- 
cellata, Sow., of the Trenton limestone, America ; and Siphonotreta micula, f. 3, 
a small species of a genus which is abundant in the Lower Silurian beds of 
Russia, is found plentifully in the trilobite-flags of Builth *. 
Lingulse, on the other hand, offer some prevailing forms. Such is L. attenuata, 
the characteristic Llandeilo fossil before alluded to, in p. 50. Its associates 
Fossils (38). Lower Silurian Brachiopods. 
I 
gula granulata, Phill. 5. L. 
tenuigranulata, M'Coy ; one j 
of the largest fossil species of I 
Lingula known in Britain ; 
with a portion nat. size. 
costata, M'Coy. 4. 
Leptaena tenuicincta, 
M'Coy; and a lateral 
view of the same. 
1. Treniatis punctata, Sow. 
2. Crania divaricata, M'Coy. 
3. Siphonotreta micula, 
M'Coy ; young and full 
grown, natural size. 4. Lin- 
are L. granulata, Foss. 38. f. 4, and a number of unpublished species. L. ovata, 
M'Coy, and L. tenuigranulata, f. 5, here figured, are conspicuous Caradoc 
species. Obolus, a genus closely allied to Lingula, is common in Russia, and, 
* As an example of the confusion which might Cambridge Museum, and published in 1851-53, 
be introduced by substituting the word Cambrian have been alone found in my original Llandeilo 
for Lower Silurian, it may be mentioned that this and Caradoc rocks, the organic remains of which 
species of Brachiopod, though collected in my were published by me between the years 1S33 and 
oldest and best-known Lower Silurian locality of 1S39. Such are :— all those fossils from the Car- 
Llandeilo flags at Builth, has been published as marthenshire localities of Llandeilo, Mandinam, 
a Cambrian fossil in the Second Fasciculus of the Goleugoed, Llangadoc, Noeth Griig; all the Breck- 
Palffiozoic Fossils of the Cambridge Museum. The nock and Eadnorshire localities, near Builth and 
reader must, indeed, be told that very many of Llandrindod ; the Montgomeryshire localities, 
the fossils to which the words ' Bala ' and ' Cam- near Welshpool and Meifod, and at Allt-yr- Anker ; 
brian ' are prefixed in that work descriptive of the Caradoc fossils from the West of Shropshire, &c. 
