KONGL. SV. VET. AKADEMIEN8 HANDL BAND. 19- N:U 6. 91 



creation ot now <feiiera, when it is known iiow this character varies in one and the 

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

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

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

 cus is seen. Of the other new genera, ranked by De Koninck with the Pleurotomaridie, 

 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., PI. decussata Sandbergek (Versteiner. d. Khei- 

 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 bo 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. 



Feed. 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 some species which have hitherto been placed 

 within the incongruous genus Eccyliomphalus, as for inst. Ecc. alatus Fekd. Roemek- 

 His Odontomaria, Leth. geogn. 4:th Ed. 1 Th. Taf. 29 iig. lU, of which he sa3's that 

 it »begreift gewisserraassen abgerollte Pleurotomarien«, is, as it, however, must be 

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

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

 p. 22, Taf. VII fig. 11^). But, as Feud. 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 occurs 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 lesi^ 

 any generic value. 



The genera Scalites, Rliaphistoma 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 fiat and even; tlie slit band situated on the acute outstandinj; anirle. 

 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 alreaciv been employed by Cn. Barrois in 18)^1 for a laniellibraiifhialc ; Ann. Soc. (SOol. 

 ilu Nord, VIII, p. 176. 



'-) rieurotomaria extensa Heiuenuain Graptolithfuhiende Diliiv. p. 18, Taf. 1 I'. 10 (= Bellcrophon cvo- 

 lutus Haupt Taf. Ill f. 13) is perhaps only an Euoinphalus. 



■') Lethita geognostica, Ed. 3, vol. I, p. 455. »Es kann jedoch Jcncr Uinstand \mi1i1 kanm zur Aufstfllirnij 

 eincr cigenen Ciattung guniigen, da schr vcrschiedenc Giistcropodcn-Gattungrn (z. B. anch Helix) (Ihilii 

 Unigsinge regelmassig veibundcn siud, ausiiahnisweise zuwuilun in Folgi; noch nicht niihcr crforschtcr 

 Einwirkungen frei wcrlcn. In keincm Fallc diiifcn solchc Arten von K\ioni])halns gL-ticnnl wcrdcn, 

 bei welchen jene Trenuuug dur Umgilngc nicht stcts, sondern nur vorherrscheiid sich liudet.» 



