90 G. LIN])TR5m, on the SILt'KlAN (iASTKoPODA AND I'TEUOI'ODA OF GOTLAND- 



uerse striai of the upper and loirrr moiety of the whorls converge in direction backvmrds. 

 In most well, preserved specimens the shell is nacreous. In some species there is a tendency 

 to fill up the apex of the shell with solid calcareous matter or even to jyartition off the 

 apex by imperforated tabuUv or diaphr<i</ms. 



Rich as this genus is in a great number of variously formed' species, ranging 

 in time from the basis of the Lower Silurians through all the Palaeozoic formations 

 with well nigh 500 species, it is conceivable, that many attempts have been made to 

 divide and subdivide it in generic groups of a second order or even only in divisions 

 of wider or uu)re narrow circumscription. Before attempting to make any such divi- 

 sions for the Gotlandic species, it may be convenient to take a review of older grou- 

 pings or of genera which may be considered as synonymic. 



As to the claims of De France as the tirst author of Pleurotomaria, it cannot 

 any longer, as Dat.l thinks, be doubted that De France really must be regarded as 

 the author and l)y almost unanimous consent also has been acknowledged as such. 

 Dall again (Preliminary Kept, on the Mollusca, Bullet. Mus. Comp. Zool. Vol. IX n:o 2 

 p. 78) considers, that Sowerby who was the first to publish its characters, is the real 

 author and that his name has to replace that of De France. But the case stands as 

 follows. The name Pleurotomaria is printed for the first time in Fehussac's Tableaux 

 Systematiques '), earlier than June 1821 and in December the same year it was characteri- 

 zed by Sowerby in his Mineral Conchology vol. Ill p. 139, pi. 278. In 1823 Ferussac 

 in a Note to the Memoir of D'Orbigny on Scissurella in the "Memoires de la vSoc. d'Hist. 

 Nat. de Paris», vol. I p. 340, says on Pleurotomaria that nee genre est connu depuis 

 longteraps des Naturalistes de Paris et son nom est deja imprime dans plusieurs ouvrages». 

 He does not name any body else but De France as the author. Moreover, James 

 Sowerby himself before 1S25, when the last pages of his »Genera of Recent and Fossil 

 Shells)) were published, in the descriptive letterpress to pi. 205, where Pleurotomaria 

 is figured, expressly states that he considered De France as the author, in saying "the 

 Pleurotomaria of De France», never mentioning himself as the author or making any 

 claims as such and (^ven not referring to his own previous description in the Mineral 

 Conchology. 



Prominent amongst the synonymic genera is Ptychomphalus L. Aoarsiz founded 

 on a shell from the Mountain Limestone, Helicina compressa Sow. It should deviate 

 from the othei's in the possession of a callosity on the umbilical centre. But De 

 KoNiNCK in his last work on the Carboniferous Fauna of Ikdgium includes in Ptychom- 

 phalus the majority of the Belgian Pleurotomaria? of that ])eriod, 59 species, and does 

 not accept the genus Pleurotomaria at all, on the ground that the first species de- 

 scribed by De France have a wide umbilicus. Now the absence or presence of an 

 umbilicus cannot, as Deshayes ^) long ago has remarked, have any influence on the 



') Tableaux Syst(';matiques des Aiiimnux Mollu3(|Ucs classes on families natuiclles, p. XXXIV. The second 

 part of tliis work, uTai)lcau Systcmnti(jue de la I'^amille des Ijiniaees" l)(;ars on its title pa{;e tlie date 

 ».Inin IS:21)). The preeedinf; pajjes i — xlvij, where Pleurotomaria is catalogued, are, eonsequeutly, 

 still older. 



■) Journal de (Jcnchyliolof^ir I p. 209. 



