118 G. LINDSTKOM, ON THE SILUKJAN GA.sTUOl'ODA AND TTEROPODA OF GOTLAND. 



at the very edge of tlie laniiual slit band turning back from the aperture, quite 

 as is the case in all Pleurotoiuariie with transverse striiu on the surface. The sujall- 

 ness of the apertural slit in this and similar species causes this dissimilarity from 

 the other Pleurotomaria.-. Around the und)ilicus a small ridge is running, a little 

 knotty where the transverse lines cross it. On the spire the transverse lines are more 

 distantiated, elevated, and formed by the lines of growth. I he aperture is circular, 

 the lips sharp and thin, not reliexed, the exterior one extending into a triangular ap- 

 pendix, a narrow groove, representing the sinus or the slit, which here is reduced to a 

 minimum. The umbilical side of the aperture is deeply insinuated, almost as much as 

 in some of the Devonian shells which D'AucniAO and Veuneuil have placed in the 

 genus Schizostoma, JSch. radiata for instance, but wliich probably are different from 

 Bhonn's Schizostoma. The umbilicus is very wide and open and all whorls are seen 

 to tile bottom of the umbilical funnel. On the umbilical side of the slit band there 

 are in some specimens discerned two or three darker spiral bands, a little deepened 

 in the shell, somewhat reminding of rests of colour bands. 



Largest specimen "26 millim. in height, 51 millim. in breadth. Another specimen 

 attains 18 millim. in height, 35 millim. in breadth, the umbilicus has i) millim. in diti- 

 meter and the slit band is 7 mill, wide across. 



This characteristic species has been found in numerous s[)ecimens in almost all 

 strata of Gotland, in the shale beds of Wisby, Westergarn and Slite, in the liujcstone 

 of Lutterhorn and Lansa of Faro, of Slite, Samsugn in Othem, Klintcberg, VVestoos in 

 Hall, Kylley, Kaleiis (^varn, Stora CarlsO, the canal of Atlingbo. 



This species has by Fekd. Koemeu been made the type of a new genus Kuom- 

 phalopterus, whicli is characterized by tubular perforations through the lamellar edge, 

 which surrounds the shell, and also penetrate through the walls of the shell into the 

 interior of the whorls. But, as stated above, there do not exist any such perforations 

 in the walls of this shell and the tubes are, as shown above, nothing but the spaces 

 between the lamellar crescents of the slit band. Nor has ever any operculum been 

 found to this species ') or to other Pleurotomaria3- There is consequently, not any reason 

 to place this in a new genus, at the highest this and tho following ones may form a 

 subijenus to Pleurotomaria. 



^o^ 



29. Pleurotomaria alata var. sulbcarinata. 



I'l. X lii;-. 33— :i7. 



This small variety differs chieily in having an obtuse ridge beneath the slit band, 

 and where it runs, the whorls arc angular, while in PI. alata, ligs. 18, II), the whorls 

 are rounded on the corresponding surface. There is a revolving ridge around the um- 

 bilicus in this, as well as in the principal form, though not in all specimens. There 

 is no reason to consider this as more than a variety of the former, as thci-e are some 



') Sec ZiTTEL llandbuch dcr I'ahcontologio Hd. 1, 2 Abth. p. 206, where lie describes ;iii opercuhiin of 

 Euoniphalopterus, but which in reality belongs to some Oriostoma. 



