AND DISTRIBUTION OF TRILOBITES. 281 
endeavours of Murchison and Sedgwick succeeded within a few 
years in throwing light upon this chaos. Murchison divides at 
present the English paleozoic rocks into two systems,—the Si- 
lurian in the West (compare Murchison’s ‘ Silurian System,’ Lon- 
don, 1839), and the Devonian in the South-west of England. 
The first he again classifies into two principal divisions and seven 
separate members. We first of all meet with, situated upon the 
lowest slates, void of fossils (upon the Cambrian system),—1,'the 
Llandeilo flags, a formation resembling the grauwacke, generally 
calcareous, traversed by veins of calespar, and containing mica, 
in which formation whole strata are filled with Ogygia Buchii; 
in its company occur the northern Battus pisiformis and Illenus 
perovalis, which I cannot distinguish from Jf. crassicauda. As. 
tyrannus very much approximates to A. angustifrons. Trinuclet 
are numerous. Llandeilo in South Wales (Caermarthenshire) is 
the classic district where this member most abounds in fossils. 
Upon this follows,— 
2. The Caradoc Sandstone*. -Abounding in Trinuclei, of 
which two occur in the Llandeilo flag (T. Caractaci and fimbri- 
atus). The Ill. perovalis also occurs again in this. Phacops 
Powisii is the Phacops sclerops of the North. It cannot be 
proved from a mere caudal shield whether Calymene punctata 
corresponds with the species of Gothland, since this form of it 
is found in several species. 
3. Wenlock shale, a slate poor in Trilobites, and correspond- 
ing in that respect with the next member; it contains Ph. cau- 
datus and mucronatus; the latter, however, is wanting in the 
limestone. 
4. The Wenlock limestone, on the other hand, has been a fa- 
yourite locality for Trilobites for ages. The Dudley fossil bears 
the name of the principal place for Wenlock fossils, and has 
carried the name of the picturesquely-situated Dudley through 
the world. Besides this fossil, the Cal. Blumenbachii, it is known 
to contain Phacops Downingiea, macrophthalmus, variolaris, cau- 
datus (incl. tuberculato-caudatus), Odontopleura Brightii, bimu- 
eronata (Parad.), Murch., qguadrimucronata (Parad.). Brontes 
flabellifer and Homalonotus delphinocephalus are likewise enume- 
rated among the Wenlock fossils; I should suppose, however, 
* Called Caradoc from a hilly range bearing this name in South Shropshire : 
the name is derived from Caractacus, the celebrated British chieftain, who 
waged war with the Romans.—Tacit. Annal. xii. 37. 
