INTRODUCTION. XX1 
found both in Germany and England, and apparently closely allied to the so-called. 
Spirifer spurius, Minster, of the Triassic marls of St. Kassian. Concluding from the 
apparent absence of congeneric species in more recent rocks, it might be concluded, 
that the Permian epoch was the last to witness the existence of the genera Cama- 
rophoria, Cleiothyris, and Strophalosia. The group Trigonotreta, whether we view it 
as divisible into two great sections depending on histological differences, connects 
the Permian system both with an earlier and a more recent period: the Triassic 
Trigonotreta fragilis, Goldf., resembles in many respects 7. Permiana, which, in its 
turn, has a striking resemblance to a carboniferous species: Zrzgonotreta cristata is 
closely related to, if not identical with, the carboniferous 7. octoplicata ; and it is also 
apparently nearly allied to a Jurassic species found at Illminster, and in Wurtemberg. 
Cleiothyris pectinifera has a few proximately related species occurring in the carbo- 
niferous rocks; such as C. expansa, C. fimbriata, C. oblonga, and C. Rorssyi. The genus 
Camarophoria, as far as is known, only conducts us to an earlier age—the carbo- 
niferous, which has yielded species (Camarophoria crumena, C. superstes) closely allied to 
one thoroughly characteristic of the Permian system, both in its vertical and its 
horizontal extent,—Camarophoria Schlotheimi, it will be remembered, having been 
found in the Mergerl-schiefer, Zechstein, and Zechstein-dolomit of Germany, as well as 
in certain of the Permian rocks in the North of England, and on the western flank of the 
Ural mountains. Camarophoria multiplicata, hitherto only found in the fossiliferous lime- 
stone of the North of England, appears to have been a local species. Hypothyris, so 
abundant inthe Protozoic, and Deuterozoic formations, is suspected to have been repre- 
sented during the Permian period ; but hitherto not a species has yet been discovered in 
rocks of this age, unless it be the so-called Zerebratula Geinitziana found by De Verneuil 
in Russia. The two species of Apithyris have undoubtedly lived in the carboniferous 
epoch; and apparently one of them (/#. suffata) either had its existence prolonged 
into, or was proximately represented during, the Triassic period. The genus Productus, 
were it not for the occurrence of two or more species in the Triassic marls of St. 
Kassian, might be said to have ceased to exist at the close of the Protozoic period : 
Productus horridus, so characteristic of the Permian rocks, was probably also a carbo- 
niferous species ; since, besides its apparently occurring in the Mountain Limestone of 
Lough Macnean, Fermanagh, there is yet to be proved the exact age of the Derbyshire 
Magnesian Limestone which yields it. The single Permian Discina speluncaria, in 
being found in the Marl-slate, compact limestone, and fossiliferous limestone, has had 
a tolerably extensive range in time. The same may be said of Lingula Credneri, 
which occurs in the Zechstein of Germany, and the Marl-slate of Durham: it appears 
to have been also found in the subordinate bed of freestone near Ferry-Hill. 
Passing to the Permian Lamellibranchs, some species have had a wide geographical 
range; for example, Plewrophorus costatus, Allorisma elegans, Mytilus septifer, Bysso-arca 
Kingiana, Monotis speluncaria, Bakevellia antiqua, and Solemya biarmica, which are found 
