INTRODUCTION. xxi 



found both in Germany and England, and apparently closely allied to the so-called 

 SjArifer sjjur'ms, Miinster, 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 ex'stence of the genera Cama- 

 roplioria, Cleioiliyris, and Stroj)halosia. 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 T. Permiana, which, in its 

 turn, has a striking resemblance to a carboniferous species : Trigonotreta crisfata is 

 closely related to, if not identical with, the carboniferous T. octoplicata; and it is also 

 apparently nearly allied to a Jurassic species found at Illminster, and in Wurtemberg. 

 Cleiothgris joedinifera has a few proximately related species occurring in the carbo- 

 niferous rocks ; such as C. exponsa, C.fimhriata, C. oblonga, and C. Roissgi. The genus 

 CamaropJioria, as far as is known, only conducts us to an earlier age — the carbo- 

 niferous, which has yielded species ( Camarophoria cnimena, C. superstes) closely allied to 

 one thoroughly characteristic of the Permian system, both in its vertical and its 

 horizontal extent, — Camarophoria ScJdotheimi, it will be remembered, having been 

 found in the Mergerl-schiefer, Zechstein, and Zech stein- dolomit of Germany, as w^U as 

 in certain of the Permian rocks in the North of England, and on the western flank of the 

 Ural mountains. Camarophoria muUijdicata, hitherto only found in the fossiliferous lime- 

 stone of the North of England, appears to have been a local species. Hgpothgris, so 

 abundant in the Protozoic, and Deuterozoic fox'mations, 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 Terehratula Geinitziana found by De Verneuil 

 in Russia. The two species of Epiithgris have undoubtedly lived in the carboniferous 

 epoch ; and apparently one of them {E. sufflatd) 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 Biscina 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, Pleurophorus costatus, Allorisma elegans, Mgtilus septifer, Bgsso-arca 

 Kingiana, Monotis speluncaria, Bakevellia antiqua, and Solemga biarmica, which are found 



