1855.] MURCHISON LESMAHAGO SILURIANS. 23 



different in grandeur and diversity of structure is the great North 

 Highland Series, when compared with the Old Red Sandstone of 

 Lanarkshire. This last constitutes, as I am disposed to believe, little 

 more than one of the three great divisions of that vast northern series 

 which is, I conceive, a full equivalent in time of all the rocks called 

 Devonian in any region of Europe. 



In Lanarkshire neither the micaceous red flagstones associated with 

 the conglomerates, nor the beds beneath or above them, have as yet 

 afforded any trace of fishes, even under the vigilant eye of Mr. 

 Slimon. If such should be discovered in the uppermost of these red 

 strata of Lesmahago, and that they be found to belong io HoloptychiuSj 

 then indeed we may infer that we have here a representative, though 

 on a very small scale only, of the upper member of the group. 

 But, not speculating further on this collateral point, I beg to conclude 

 with a very few observations upon the Crustacean beds of the newly 

 discovered Upper Silurian rocks of Scotland. 



Rising out as these dark grey beds do, upon the Logan Water banks, 

 from beneath the Lower Old Red, they occupy precisely the same 

 horizon as that uppermost zone of the Silurians of Shropshire and 

 Herefordshire which includes the bone-bed and the Downton Castle 

 building-stone, and to which, as it graduates up into the Old Red, the 

 name of *' Tilestones " has from its flaglike character been given. 



Near Ludlow, Hereford, and several other places, the thin course 

 with small fish-bones has been traced over an extensive area, and 

 in several places where the fishes are wanting the band is still well 

 characterized by the associated large Crustaceans, chiefly Pterygotus. 

 Recently Mr. Banks has discovered in those strata near Kington 

 which I formerly referred to this age, some very beautiful forms of 

 this genus, of which he sent me the drawings and descriptions, and 

 which have been submitted to the Society. Together with the Pte- 

 rygoti Mr. Banks found fossils formerly confounded with the genus 

 Cephaluspis, Ag., but now separated. The species are new, but much 

 like C. Itloydiiy Ag., hitherto known only in the overlying Old Red. 



Large Crustaceans of the group of EurypteridcB * (Burmeister), to 

 which the Pterygotus belongs, have also been found in the Tilestones 

 of Westmoreland, and it is curious to observe that in most of these 

 localities they are accompanied by the small Lingula cornea (Sil. 

 Syst.) of the Ludlow district. 



In Podolia similar large Crustaceans analogous to Pterygoti were 

 found in strata rising out from beneath rocks which are known to be 

 of Devonian age, and to these Dr. Fischer gave the name of Eury- 

 pterus tetragonophthalmus. Recently M. Eichwaldf has detected 

 several of these large Crustaceans, one of which he figures as JEury- 

 pterus remipes, Dekay, in the Isle of Oesel in the Baltic, — i. e. in 

 a limestone which my colleagues and myself referred to the highest 

 Silurian stage ; so that in the North as in the South of Russia, the 

 zone under consideration, when clearly exposed, is everywhere cha- 

 racterized by large and peculiar Crustaceans of this group, no one of 

 which has ever been found low in the Silurian rocks. 



* See Palseoz. Fossils Cambridge Museum, Fasc. 1. 



t Bull. Soc. Imp. Nat. Moscou, 1854, vol. xxvii. p. 100, 



