110 G. LINDSTKÖM, ON THE SILURIAN GA.STUOFODA AND rTEROrOIM OF GOTLAND. 



4. Pleurot. sp. {—? Eccylioitiplialuw alatus Koemeu, ? Holicites ccntrifugus Wah- 

 LENBEKG, sec also Pl. XV, iig. 12 — 14 in »Fragmciita Silurica). This is u smaller specics 

 thuii the former, more uiieoiled and tending to complete scalarid formation. The in- 

 sidc of the vvhorls is not so steep as in Pl. niarginata and the funne) formed on the 

 apical side not so regular as in that. The sculpture is more distinct of eoarse trans- 

 verse lines and the slit band is more prominently alate or lamiriar thau in them. This 

 occurs ill the Lower Gray Urthoceratite limestone, in the Upper Red and Upper Gray 

 Orthoceratite limestone and also in the Chasmops limestone of Oland. 



It is of such forms as this, that the genus Eccyliomphalus has beeu built up, 

 eommingled with others, as evohite Euomphali. To elucidate their distribution in 

 time the following table may serve. 





Lowev Red 



Orthoc. 

 Limestone. 



Lowei- Gray 



Orthoc. 

 Limestone. 



Upper Rud 



Orthoc. 

 Limestouc. 



Upper Gray 



Orthoc. 

 Limestone. 



Chasmops 

 Limestone. 



Youngest 

 Limestone 

 of Öland. 



Lepta;na 

 Limestone 



of 

 Dalecarlia. 



Shale 



of 



Gotland. 



* 



* 



* 

 * 

 * 



* 



* 



* 



* 



V 



* 

 * 





* 



2 Pl. obvallata Wahl.. 



3 Pl. margiuatii Eichw 



4 Pl. spJ) 



Divisio IV. SIMPLICES, 



21. Pleurotomaria Ivalida n. 



Pl. IX fig. 11—13. 



Shell elongate, turbinated, with seven or seven and a half whorls, whieh are ven- 

 trieose, the superior ones^forming an obtuse angle midway between the median line 

 of the whorl and ihe suture where the slit band is situated. 



The whorl is almost flat beneath the slit band sloping suddenly inwards towards 

 the suture. There are only some slight traces left of the sculpture of this uncom- 

 monly thick shell, and it consists in transverse striaj. The slit band is very large, 

 nearly 4 mill. across, the height of the whorl being 27 mill. The aperture is oblong 

 and the columellar lip thick and reflexed, so as to hide the umbilicus of whieh there 

 is no trace, as the columella is solid. The shell seeras to have been niuch exposed and 

 weathered before it was enclosed in the limestone. 



It has been found in a härd, crystalline limestone near Lillugn in a wood between 

 the parishes of Ardre and Älskog. Pl. infläta Mac Coy, Sil. Foss. of Ireland p. 15 

 pl. 1 f. 15, somewhat resembles this shell in form. 



') Pl. replicata, nearly related ta this, is found in the Gotland shale. 



