KONGL. SV. VET. AKADEMIENS UANDLINGAU. BAND. 19. N:o 6. 5 



In spite of tlie certaiiity of luany unavoidable failiiigs and shortcoiuiiigs, wliicli 

 as pointed out abovc, foUow from tlie iiature and conditions of the material, I ventu- 

 red to take up this study wlieii it was found how unexpectcdly rich and vai-ied were 

 the forms entoml)ed in tlic Siluriari strata of Gotland, and tlianks to tlie inuniiicence 

 of the Ro)'al Swedish Academy of Sciences it has novv been brouglit to its conclusion. 

 Though fragmentary in many respects tliis niemoir may serve in some degree as a star- 

 ting point for future labours in the same field. 



Silurian strata of Gotland. 



Before entering any further into the minor details of the composition of the 

 Gastropodan Fauna, it may be proper to survey the physical conditions, in which 

 the shells are found, as the strata, rocks and localities and also to inquire into their 

 general faunistic characters. Through the classical researches of Hisinger the general 

 features of the geological constitution of Gotland were very well known ; but it was not 

 until the visit of Sir Roderick Murchison to the island in 1845 that the position 

 of its strata was interpreted according to the researches, which were then carried on 

 in other parts of Europé and especially in England by Murchison himself. After a 

 stay of a few days, chiefly on the west coast of the island, he proclaimed the strata as 

 Upper Silurian and arrived at the conclusion that they were to be subdivided into 

 three groups, corresponding to the English Wenlock, Aymestry and Upper Ludlow, and 

 that in fact the southernmost point with its substratum of sandstone was the youngest 

 division, in direct opposition to Hisingee, who considered the sandstone as the oldest 

 of the whole of the strata and underlying them all, though hidden from view north of 

 Bursvik. The conclusions of Murchison were adopted by Friedrich Sciimidt, who fol- 

 lowed up his researches and gave a more complete description. He also divided the 

 island in three groups: Northwest Gotland or the Wisby Zone, Central Gotland and South 

 Gotland, subdividing the second or Central Gotland in two beds, that of Pentamerus estho- 

 nus and Pent. conchidium, a division which cannot be upheld as Pent. conchidium oc- 

 curs beneath P. esthonus as well as above it and moreover is restricted to vei"y narrow 

 limits within the large zone he has assigned to it. lie assumed the strike of the strata 

 to be N. E. and S. W. and their dip consequently from N. W. to S. E. His three 

 groups form oblique belts across Gotland. He, as well as Murchison, had only pahi?on- 

 tological evidence to adduce in favour of his opinion. Murchisons, and consequently 

 also Schmidts views have been contested, amongst others by Ferd. Roemer and Hel- 

 mersen, and it is highly probable that their mode of viewing the stratification of Got- 

 land is more consistent with the real state of the facts than that of the former geo- 

 logists. As Roemer and Helmersen have already demonstrated, there are neither stra- 

 tigraphical nor palaBontological evidences to support the views of Murchison and Schmidt. 

 If, as the latter authors hold it, the shale along the west coast of Gotland belongs to at 

 least two divisions, namely the beds around Wisby to the Wenlock shale and those south of 

 Klintehamn to the Lower Ludlow, the superposition of these strata above each other 

 must of necessity be seen somewhere. But as to the shale beds of Wisby they can be 



