118 G. LINDSTRÖM, ON TlIE SILUKIAN GAöTHOPOIJA AND PTEKOPODA OF GOTLAND. 



ut the verv c;dgc of tlie luiuiniil slit hund tuniiiig biick from thc aperture, (juite 

 as is the cuse iu all Pleurotomariii; with traiisversc strio) on tlie surfacc. The siuall- 

 ness of tlie apertural slit in tliis and sinulav species causes tliis dissiniikirity from 

 the other Pleui-otomariiu. Around tlie uinbilicus a suuill ridge is runniiig, a little 

 kuotty where the transverse lines eross it. On the spire the transverse lincs are luore 

 distantiated, elevated, and formed by the lines of growth. Ihe aperture is cireular, 

 the lips sharp and thin, not reflexed, the exteriör one extending into a triarjgular ap- 

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

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

 in some of the Devonian shells which D'ARCiiiAC and Verneuil have placed in the 

 genus Schizostoma, Sch. radiata for instance, but which probably are differcnt from 

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

 to the bottom of tiie 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 9 millim. in dia- 

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



This characteristic species has been found in numerous specimens in almost all 

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

 of Lutterhorn and Länsa of Fårö, of Slite, Samsugn in Othem, Klinteberg, Westöös in 

 Hall, Kylley, Kålens Qvarn, Stora Carlsö, the canal of Atlingbo. 



This species has by Ferd. Roemek been made the type of a new genus Euora- 

 phalopterus, which is characterized by tubular perforations through the lameilar edge, 

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

 interiör 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 lameliar crescents of the slit band. Nor has ever any operculum been 

 found to this species ^) or to other Pleurotomariaa- There is consequently, not any reason 

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

 subjjenus to Pleurotomaria. 



'o^ 



29. Pleurotomaria alata var. subcarinata. 



Pl. X fig. 33— .37. 



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

 and where it runs, the whorls are angular, while in Pl. alata, figs. 18, 19, the whorls 

 are i-ounded 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 there are some 



') See ZiTTEL Handbucb der Paliieontologie Bd. 1, 2 Abtli. p. 206, where lie describes an operculum of 

 Euoinphalopterus, but which iu reality belongs to some Oriostoma. 



