96 G. LINDSTROM, ON THE SILURIAN GASTROl'ODA AND I'TKIUH'dDA OF GOTLAND. 



2. Pleurotomaria gradata n. 



PI. VII ligs. 26—27. 



Shell (•(iiiical, trocliit'onn, si^ire hliint, broad, wliorls eight with regularly straight, 

 sloping sides of faint convexity, ahruptedly bent along the superior suture through 

 the vertical and almost even zone around the slit band. This band is central on the body 

 whorl and remarkable as being one of tlie narrowest amongst all the Silurian Pleuro- 

 toinariaj and periia])s amongst all known. It is reduced to a narrow fissure, a mere frac- 

 tion of a millimetre and thin as a knife edge. It continues open a long way round 

 the body whorl and the next, and then at last is tilled up. But owing to its narrow- 

 ness it is impossible to discern any crescents on it. Like the related, preceding one, 

 the slit band is enclosed within a separate zone, differently ornam(;nted from the other 

 surface and bordered by a narrow line on each side. In this median held there are 

 onl)7 transverse lines crossed by a few, obscure, longitudinal ones. On some distance 

 a blunt ridire is runniu": on each side. The ornamentation of the whorls consists of 

 somewhat distantiated, transverse lines, connected by more narrow spiral ones and 

 parallel to the slit band; in the interstices microsr-opieally minute transverse lines an? seen. 

 The belt around the slit band does not form any prominent ridge as in the former 

 species, but rather a somewhat concave or straight facet on the whorl. The suture is 

 shallow. The aperture is rather more broad than high, its columellar lip is strongly 

 reflexed around the open umbilicus. 



Height 22 millim., breadth 20 millim. Apical angle ()9°. Another specimen has 

 24 millim. in height and 23 mill, in breadth. Found in numerous specimens in the 

 limestone of Sandarfve kiille and also in the gray limestone of Linde kulle. 



Oehlert has described a PI. Virensis from the Lower Devonian of France, and 

 this comes near to our species through its ornamentation and the slit band, though 

 its spire is lower. 



3. Pleurotomaria Linnarssoni n. 



PL XX fij?. 21—24. 



Shell small, discoid, s\n\•^\ moderately prominent, wliorls six, increasing in size 

 slowly and proportionately. They arc adorned with a delicate network, on the apical 

 side consistinc of intercrossinir stria' of which the transverse ones are directed back- 

 wards in an acute angle against the slit band. At the intcsrcrossing of these lines 

 small nodules are formed giving the surface a prickly appearance, with small pits in 

 the interstices. The slit band is placed below a narrow keel which divides the shell 

 exactly in two halves. It is exceedingly narrow and accompanied on both sides by 

 longitudinal lines, which are more ])rominent than th<' others. On the umbilical side 

 the whorls are more ventricose than on the opposite and also similarly ornamented. 

 The aperture is circular and the umbilicus isjarge and open. H. 4 mill., br. 8 mill. 



