PALAEOZOIC FOSSILS. 
141 
Whilst the general arrangement of the fossils is stratigra- 
phical, there is under each formation a subordinate zoological 
classification of the invertebrata, commencing with the simpler 
forms of life. 
THE LOWER GALLERY. 
This Gallery contains the fossil plants and invertebrata of the 
palaeozoic strata, and also, the pleistocene vertebrates. The 
latter have been placed here, in consequence of the difficulty of 
finding space for them with the pleistocene invertebrata on 
the floor above. The general series of fossils may be con- 
veniently studied by commencing with the Flat Cases on the 
Gallery-rail at the head of the western staircase. 
Against the opposite wall is placed a polished block of serpen- 
tinous limestone from the Laurentian rocks of Canada, contain- 
ing the curious structure called Eozoon. This has been regarded 
by some authorities as a gigantic reef-forming foraminifer of 
peculiar interest, as representing the oldest known form of life. 
Its organic nature, however, is now usually denied. There is 
still some uncertainty respecting the true organic grade of the 
branched structures termed Oldhamia which occur in Cambrian 
rocks near Dublin and rank among the most ancient traces of 
life yet found in the British Isles. Worm-burrows and castings 
are met with in these and in many other ancient rocks, as in 
the Longmynd rocks of Shropshire, and notably in the Gambrian 
quartzites and limestones of the north-west of Scotland. 
Among the oldest organic remains, often fragmentary and 
ill-preserved, are those of the extinct crustaceans well known as 
Trilobites. Numerous examples will be found in the Flat 
Cases, serving to illustrate their great diversity in size, shape 
and structure. The Cambrian strata have, in recent years, been 
arranged in zones, named, according to their typical trilobites, 
the Olenellus, the Paradoxides, and the Olenus zones. A 
conspicuous fossil in the first Flat Case is the large Paradoxides 
Davidis from the Menevian beds — a group of beds which borrow 
their designation from Mencevia, the classical name of. St. 
David’s. 
The Lingula flags, which occur above the Menevian beds, 
derive their name from the little brachiopod called Lingulella 
Davisii, closely akin to Lingula. This type is remarkably 
persistent, the horny shell of the living lingula being extremely 
similar to the Cambrian fossil. The brachiopods, comparatively 
rare at the present day, are a group of great importance in the 
Palaeozoic and Secondary strata. The Lingula flags are 
followed by the Tremadoc beds, so named from the locality in 
North Wales where they are characteristically developed. 
The Angelina Sedgwickii, from these slates, is a trilobite 
notable for the distortion which it has, in many cases, suffered 
by earth-pressure. 
