KONGL. SV. VET. AKADEMIENS IIANDL BAND. 19- NIO 6- 91 



creation of new genera, when it is knowii how this character varies in one and tlie 

 same species and that, nioreover, a single character seldom is so important as to 

 distinguish a genus. Amongst the species of Ptychomphalus, established by De Koninck 

 there are several without any callosity at all, and also others wliere a narrow umbili- 

 cns is seen. Of the other new genera, ranked by De Koninck with the Pleurotomaridai, 

 such genera as Baylea, Worthenia, Rhineoderma do not show the least trace of any 

 slit band to judge from the figures, the descriptions and in some instances by such 

 specimens of them as I have seen. The genus Agnesia again seems to have been 

 founded only on the distinction of its being sinistral, but as it in other details agrees 

 with Pleurotomaria and sinistral as well as dextral specimens occur within the same 

 species of Pleurotomaria, as, for inst., Pl. decussata Sandbeuger (Versteiner. d. Rhci- 

 nischen Schichtensystems p. 197, tab. 24 f. 2), there seems not to be valid grounds 

 to create a new genus out of it. The same may be said in reference to Gosseletia '), 

 Mourlonia and Luciella as none of them has such prominent or permanent characters 

 as to entitle them to any generic distinction from Pleurotomaria. 



Ferd. Roemer's Euomphalopterus, however aberrant, is nothing but an extreme 

 form of Pleurotomaria, as will be shown further down. The extraordinary develop- 

 ment of the slit band is shared by sorae species which have hitherto been placed 

 within the incongruous genus Eccyliomphalus, as for inst. Ecc. alatus Ferd. Roemer- 

 His Odontomaria, Leth. geogn. 4;th Ed. 1 Th. Taf. 29 tig. 10, of which he says that 

 it »begreift gewissermassen abgerollte Pleurotomarien», is, as it, however, must be 

 conceded, more straight than any other. As further instances of such PleurotomaridaB 

 may also be cited Pleurotomaria centrifuga F. Ad. Roemer, Verstein. des Harzgebirges 

 p. 22, Taf. VII tig. 11^). But, as Ferd. Roemer himself long ago remarked '), the forma- 

 tion of scalarid shells can only have a subordinate value as a generic characteristic, 

 as there are involute or evolute specimens belonging to the same species as we shall 

 see in the description of Pleurotomaria qualteriata. The same peculiarity in the 

 growth of the shell occui'S also, as is already shown, in Platyceras and even in Euom- 

 phalus, without there being any grounds to ascribe to it specific, so much the less 

 any generic value. 



The genera Scalites, Rhaphistoma and Helicotoma are founded chiefly on American 

 fossils and belong to the group of Pl. qualteriata, having the whorls on the apical 

 side more or less flat and even; the slit band situated on the acute outstanding anglc; 

 which is formed where the apical and the umbilical sides meet. Most authors seem 

 now to agree that all are identical and coincide with Pleurotomaria. 



') This name has alreadv been employed by Ch. Barrois in 1881 for a lamellibranchiate ; Ann. Soc. Géol. 

 du Nord, VIII, p. 176. 



-) Pleurotomaria exteusa Heiuenhain Griiptolithftlhrende Diluv. p. 18, Taf. 1 i'. 10 (= Bellero])lion evo- 

 lutus Haupt Taf. III f. 13) is perhaps only an Buoraphalus. 



•') Lethoea geognostica, Ed. 3, vol. I, p. 455. »Bs känn jedoch jener Umstand wohl kaum zur Aufstellung 

 einer eigenen Gattung geniigen, da sehr verschiedene Gasteropodcn-Gattungen (z. B. auch Helix) deren 

 Umgänge regelmässig verbunden sind, ausnahmsweise zuweilen in Folgc nocli nielit näher crforschter 

 Einwirkungen frei wer'len. In keinem Falle diirfen solche Arten von Euoraphalus getrennt werden, 

 bei welchen jene Trennung der Umgänge nicht stets, sondern nur vorherrschend sich lindet.» 



