90 G. LINDTRÖM, ON TllE SILUKIAN (iASTROPODA AND l'TKK01'01M (W GOTLAND- 



ver.se strios of the upper and lower moiety of the whorls converge in direction backwards. 

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

 to Jill up the apex of t/ie shell with solid calcareous matter or even to partition of the 

 apex by imperforated tabulce or diaphragms. 



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

 in time from tlie basis of the Lower Silurians through all the Pala30zoic 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 more 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 first author of Pleurotomaria, it cannot 

 any longer, as Dall thinks, be doubted that De France really must be regarded as 

 the author and by almost unanimous consent also has been acknowledged as such. 

 Dall again (Preliminary Rept. 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 stånds as 

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

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

 zed by Sowerby in his Mineral Couchology vol. III p. 139, pl. 278. In 1823 Férussac 

 in a Note to the Meraoir of D'Orbigny on Scissurella in the »Mémoires de la Soc. d'Hist. 

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

 longtemps des Naturalistes de Paris et son nom est déjä imprimé 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 pl. 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 even not referring to his own previous description in the Mineral 

 Conchology. 



Prominent amongst the synonymic genera is Ptychomphalus L. Agassiz founded 

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

 from the others in the possession of a callosity on the umbilical centre. But De 

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

 phalus the majority of the Belgian Pleurotomariaj of that period, 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 Systématiques des Animaux Mollusqucs classés en familles naturelles, p. XXXIV. The second 

 part of this work, "Tableau Systématique de la Famille des Limaces" bears on its title pagc the date 

 »Juiu 1821». The preceding pages i — xlvij. where Plenrolomaria is eatalogued, are, consequently, 

 still older. 



-) Journal de Conchyliologie I p. 209. 



