KONGL. SV. VET. AKADEMIENS HANDL. BAND. 21. N:0 9. 5 



variable forms of P. bilobus approach very closely to P. osiliensis of Gotland and 

 Oesel. In Oesel, again, remains of Pter3'gotus have also been found in the beds of 

 Rootzikiill, which belong, according to Fr. Schmidt, to the base of the highest beds of 

 the Upper Silurian. Also in Podolia, Galizia and Boheinia various species of Ptery- 

 gotus occur in the highest or nearly the highest strata of the Upper Silurian. The 

 same is also the case in the United States, where the Pterygoti, together with species 

 of Eatonia and Strophomena, nearly related to those from Wisby, are found in the 

 highest Upper Silurian beds near the limits of the Devonian. As in Oesel, the Got- 

 land beds containing Pterygotus, are overlaid by massive limestones with a maximum 

 thickness of 100 feet, which are in fact the newest palffiozoic strata of the island. By 

 MuRCHisoN these limestones were regarded as low down in the Silurian series, so as 

 to be coéval with the English Wenlock'), Avhilst he believed the strata more to the 

 south to be more recent and to correspond to the Ludlow. In a similar manner. Fe. 

 Schmidt coordinates the beds near Wisby with the oldest beds in Oesel, and states that 

 only the most southern beds of Ohhesare pank and Rootzikiill are the equivalents of 

 the Silurian of Östergarn and Hoburg. Now it would be a very stränge and almost 

 unaccountable fact, if the same species, Pterygotus osiliensis, which has a very limited, 

 vertical distribution both in Oesel and Gotland, should in the former island be found 

 in beds of Ludlow age, whilst in Gotland it should appear in beds which by Murchi- 

 SON and Schmidt^) are regarded as Wenlock, and not at all in those beds which these 

 authors call Ludlow. 



As this Pterygotus and its kindred forms are found everywhere else in beds of 

 Ludlow age, and as, moreover, a Scorpion, nearly related to that found in Gotland, 

 has also been found in Scotland, together with Pterygotus, I think, that the whole 

 series of the Upper Silurian formation, which in other countries attains so great a thick- 

 ness, is represented in Gotland by the shale and limestone beds, which near Wisby 

 do not exceed a thickness of about 200 feet. The lowest shale beds north ofthistown 

 are filled with Stricklandinia lirata and may thence be designated as of Upper Llan- 

 dovery age. The superimposed principal mäss of the shale and the intermediate strata 

 correspond to the Wenlock beds, whilst the beds of limestone, shale and clay at a 

 height of 120 feet must be regarded as representing the Ludlow series of other coun- 

 tries. The highest limestone, at least 60 feet in thickness near Wisby, and much thicker 

 in other places, contains such undoubted Silui-ian fossils as Crotalocrinus, beds of Tri- 

 merella and Megalomus, and ■ consequently belongs to a more recent portion of the 

 Ludlow series. There are no beds of newer age than the limestones in the north of 

 Gotland, and the idea formerly entertained that they were overlaid by låter beds, must 

 be given up, since the beds in the South of the island have been clearly demonstrated 

 to be merely a continuation of those to the North. 



The thin seam of clay in which the Scorpion was found is of a light-grayish 

 colour, and of a v ery soft and earthy character. On the same piece which incloses the 



1) Silurian Eooks of Swedeii (Qii. Journ. Geol. Soc. 1847 p. 19 — 20). He placed, contrary to Priedr. 

 Schmidt, the rocks of Fårö and Slite also in tlie Wenlock series and says: »not a shadow of doubt could 

 exist respecting the age of the great mäss of limestone and shale of the north of Gotland» . . . 



^) Beitrag zur Geologie der Insel Gotland. Dorpat 1859. 



