KONGL. SV. VET. AKADEMIENS HANDL. BAND. 19. N:0 6. 



117 



Euomphidus alatus 



Schizostoma alatum 

 StraparoUiis alatus 

 Pleui-otomaria alata 

 Euomphalopterus alatus 



1851. Moiuus Brit. Fossils Ed. 2, 247. 



1855. PicTET Tniité de Pal. III, 155, pl. LXll f. 12. 



18G2. Mac Coy Synopsis Sil. Foss. Ireland, 13. 



1867. Salteii Sikiria 3 Ed., 531, pl. 25 f. 4. 



1867. LiNDSTiiÖM Nomiiia foss. Gotl., 23. 



1867. QuENSTEDT Haiulbucli der Petnifakluiiktmdc, 506, tab. 45 f. 64. 



1868. BiGSBY Thesaurus Silurious, 153. 



•1871. Baily Figures of Cliaracteristic British Fossils pl. 111, pl. 21 f. 7 (scarcely), 



1873. Saltek Cat. Cambr. Mus., 157. 



1882. QuENSTEDT Petrefakteiikuiide Deutsclilauds l:e AbI.li. 7:e Bd., 327, tab. 197 T. 



1842. U'Archiac & Veen. Träns. Geol. Soc. Lond. 2;d Ser. vol. VI, 366. 



1850. ©'Orbigny Prodr. I, 29. 



1858. Fr. Schmiut Estliland, 201. 



1876. Feku. Koemer Leth. Geogu. tab. 14 f. 9 a — 9 b. 



41. 



Shell turbinute, spire broad and short, corisisting of six or seven tubulur wliorls, 

 circular in section, lig. 29. The slit band is placed above the median line of" the 

 whorl, nearly on a level with the upper edge of the apertnre. This large, laniellar 

 slit band, whieh is built on an exactly honiologous plan with that of Pleur. replicata 

 and Pl. limata, occupies a belt around the shell, which on the last whorl attains a 

 length across of 12 millni. in the largest specimens, the wliole diameter being 50 mm. 

 It is directed at first obliquely upwards, lig. 29, 30, and turns at the exteriör edge 

 abruptedly downwards in a curve, which sometimes has the appearance of a hook, f. 30, 

 32. Along its outermost margins this lamina is in some specimens folded in undulations 

 f. 24. If this large slit band be split in two halves along its median line, it is found 

 on each side to consists of two thin strata (f. 27) the exteriör one transversally stria- 

 ted on its surface and the interiör one qnite smooth and transparent. Within these 

 are enclosed the crescentic laminie and through their development the space between 

 the bordering lamina; seenis to be divided into a number of narrow compartinents 

 (lig. 27, the enlarged portion). They are wider apart near their exteriör eiids and 

 converging towards the whorls. When the slit band is sectioned transversally across 

 these crescents the appearance shown in lig. 30 is produced. The curved outlines of 

 ten obliquely sectioned, crescentic lamelke are seen in the dark shale between the 

 bordering edges of the slit band. These enclosing lamellai are in direct continuation 

 with the exteriör darker stratum of the shell, composed of minute, angular laminaa. 

 Within this exteriör stratum another of clear crystalline calcite lies, often retaining a 

 nacreous lustre. There are absolutely no Communications, nor perforations or tubes 

 between the interiör cavity of the whorls and the spaces separating the ci'escentic lamella3 

 of the slitband as Ferd. Roemek has supposed. The interiör cavity is closed as in 

 other Pleurotomaria3. Along the exteriör edge of the slit band, lig. 31, the ends of 

 the crescents are discerned, especially when a little cut; the thin edges of the band 

 are usually broken on the older whorls, f. 22. 



The umbilical side of the shell is nearlj^ cup shaped, being hemmed in around 

 the edges by the high, turned up slit baiid and sunk towards the umbilicus, around 

 which there is an elevation. 



The surface is only transversally striated, the stria; running straight down to 

 the slit band and, chielly on the umbilical side, directed towards the aperture and 



