KONGL. SV. VET. AKADKMIENS IIANDL. BAND. 19. N:0 6. 89 



According to the definition lirst given by De France all those palteozoic species, 

 which have the characteristic, broad slit which by and by during continued growth is 

 filled up and changed into the equally characteristic slit band, are numbered amongst 

 them. This family is thus made to contain the following eight palreozoic genera, viz. 

 Pleurotomaria, Murchisonia, Odontoinaria, Brilonella, Porcellia, Catantostoma, Polytre- 

 maria and Trochotoraaria. Of these only two, Pleurotomaria and Murchisonia, are re- 

 presented through species in the Silurian formation of Gotland, but in such a large 

 nuniber that they make up nearly a third of the whole fauna of Gastropoda. 



The limits between this family and the following, that of the Euomphalidse, 

 are somewhat obscured through such forms as Pleuronotus (Euomph.) Decewi, in which 

 there is an approach to the formation of a complete slit band, in connection with a 

 general form of the shell as in Euomphalus. It is although questionable whether one 

 of the specimens^) figured by James Hall and in which the slit band is most promi- 

 nent really belongs to the same species or to Euomphalus at all. 



There are also some shells which have been placed in this family, though thej^ 

 sometimes exhibit a change of a regular and distinct slit band into the simple, notched, 

 angulate rib, such as is characteristic of the Euomphali. Pleurotom. planorbis His. 

 for instance thus forms in a certain degree a connecting link between both families. 

 But in consequence of such structural variations some confusion bas been unavoidable 

 and some uncertainty ensued which genera are to belong to this or the following fa- 

 mily. Moreover, genera, which do not at all show the characteristic features, have 

 been placed amongst the Pleurotomaridaj, and, again, others, which of necessity must 

 be numbered with them have been excluded. An attempt to clear up this somehow 

 is made further down, when the respective genera are treated. 



Gen. PLEUROTONIARIA De France. 



1810? Hercoles Montfort p. p. Conchyl- System. II, 274. 



1810 Anatomiis Monti'. p. p. ibid. 278. 



1821 Pleurotomaria De France in Férussac Tableaux Systématiques, p. XXXIV. 



1823 Scissnrella LVOrbigny p. p. Mém. Soc. II. N. Par. vol. 1, ,340. 



1825 Pleurotomarium Blainvili,e Malacologie, 429. 



18.37 Inachus His. p. p. Leth. Suec, 37. 



1837 Ptycliomphalus L. Agassiz Gross-Britanniens Mineral. Connli. 23, 222. 



1842 Scalites Conrad p. p. in Emmon's Geol. Rept. 312. 



1847 Rhaphistoma Hall Fal. N.-York I, 28. 



1859 ITelicotoma Salter Figures and Descript. of Oanadian Organic Reraains, Dec. 1, 10. 



1876 Etiomphalopterus Ferd. Roemer Letli. Gnogn. Ed. 4. l:e Theil, Taf. 14 fig. 9. 



1883 Gosseletia De Koninck Faune Carbonif. Belg. II, pt. 4, 28. 



1883 Ågnesia Ii). Ibid. 99. 



1883 Luciella Id. Ibid. 107. 



1883 MourlonialT). Ibid. 245. 



Shell of varying shajye, trochiform, turhinated, discoid nr glolmlar, nnth a hroad 

 angid.ar slit near the middle of the exteriör Up, continued on the whorls by n band^ which 

 is bordered by one or two elevated lines on each side and tovmrds which the trans- 

 1) Pal. of N.-York, vol. V, pt. II, pl. 29 fig. 7. 



K. Vet. Akad. Handl. Band 19. N:o 6. '-^ 



