KONGL. SV. VET. AKADKMIENS IIANDL. BAM). 19. N:<) 6. 89 



According to the definition tirst given by De France all those pala'ozoic 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 palaeozoic genera, viz. 

 Pleurotomaria, Murchisonia, Odontomaria, Brilonella, Porcellia, Catantostomn, Polytre- 

 maria and Trochotomaria. Of tlu-se only two, Pleurotomaria and Murchisonia, are re- 

 presented tlirough si)ecies in the Silurian formation of Gotland, but in such a large 

 number that they make up nearly a third of the whole fauna of Gastropoda, 



TIu! limits between this family and the following, that of the Euoinplialida"!, 

 are somewhat obscured through such forms as Pleuronotus (Euoniph.) 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 the)' 

 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 has been unavoidable 

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

 mily. Moreover, genera, which do not at all sht)w the charatiteristic features, have 

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

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

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



Gen. PLEUROTOMARIA l)i. France. 



1810? Hercnles Montfort p. p. Oonchyl. System. II, 274. 



1810 Anatomns Monti', p. p. ibid. 278. 



1821 Plfiirotomririn De France in Fkrussac Tableaux Svstt-matii|iies, p. XXXIV. 



1823 Snissurdla D'Orbiony p. p. M6m. Soo. H. N. Par." vol. 1, .340. 



182.5 Pleurotnmarium Bi.AiNvn.i.E Malaoologie, 429. 



1837 Inarhus His. p. p. Lath. Suec, 37. 



1837 Pti/chompfialiis L. Aoassiz (iross-Britaniiiens Mineral. Cnnolr. 23, 222. 



1842 St'alitef: Oonrah p. p. in Kmmon's Oeol. Kept. 312. 



1847 Rhaphistoina IIali. Pal. N.-York 1, 28. 



18.59 lli'licotoiiia Salter Figures and De.ieript. of Canadian Orffauic Remains, Dec. I, 10. 



187ri Enomphnlopteru.i Ferd. IJoemek Letli. Oeogn. Ed. 4. l:e Tlieil, Taf. 14 tig. 9. 



1883 riosselctia Df. Koninck Faune Carlionif. Relg. II, pt. 4, 28. 



1883 Aijnenia li). Ibid. 99. 



1883 LucieUa Id. Ibid. 107. 



1883 Monrlonialv. Ibid. 24.'). 



SIipII of imryinfi ftlidpe, trnchiform , turhinnlcd, di^roul or (/lohnlrir. n-ifJi a hroail 

 onf/nlar shf ni'itr ike middle of f/ir r.rlcrior liji, covliviii'tl oii flu' irhorh lii/ a Imnd^ ir/iicJi 

 is bordered, hy one or l>ro elfvated lines on eae/t side and toirards vliich the trans- 



') Pal. of N.-Yovk, vol. V, pt. II, pi. 29 Hg. 7. 



K. Vet. Akail. Haudl. B,and 19. N:o li. 12 



