KpNGL. SV. VET. AlvAlJEMlENH IJANDI.INGAI;. liANI). 19. N:() 6. 5 



In spitr of tlic iLTtaiiity of luaiiy uiiiivuidabk' failings and ,sliortc<)iiiinir.s, wliicli 

 as pointed out above, follow from the nature and condition.s of the material, 1 ventu- 

 red to take up this study when it was found how unexpectedly rich and varied were 

 the forms entombed in the Silurian strata of G(jt!and, and thanks to the muniiicenee 

 of the Royal Swedisli Academy of Sciences it has now been brought to its eonclusiou. 

 Though fragmentary in man}' respects this memoir nuiy 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 pro])er to survey the physical conditions, in which 

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

 general fauni.stic 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 Mukchisun to the island in 1845 that the position 

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

 in other parts of Europe and especially in England by Murcuison 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 tliat 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 Hisinger, who considered the sandstone as the oldest 

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

 Bursvik. The conclusions of Murchison were adopted by Friedrich Schmidt, wlio fol- 

 lowed up his researches and gave a more complete (lescri})tion. He also divided the 

 island in three groups: Northwest Gotland or the VVisb}' 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 very narrow 

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

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

 groups form oblique belts across Gotland. He, as well as Murchison, had only pahvon- 

 tological evidence to adduce in favour of his oj^inion. Murchison's, and consequently 

 also Schmidt's views have been contested, amongst others by Ferd. Roemer and Hel- 

 MERSEN, and it is highly probable that their mode of viewing the stratiiication 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 palajontological 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, namel}^ the beds around W'isby 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 



