i6i 



JOURNAL OF CONCHOLOGY. 



Vol. 14. APRIL, 1914. No. 6. 



CLAUSILIA DUBIA Drap.^ AT DOVER. 



By J. DAVY DEAN. 



(Read before the Societj-, December loth, 1913). 



" Draparnaud separated Miiller's Clausilia perversa into two species, 

 giving to them the names C. rngosa and C. diibia, and Moquin- 

 Tandon followed Draparnaud, substituting the name nigricans for 

 dubia, assuming on the authority of Dr. Gray that it was so named by 

 Pulteney in 1 799. This is a mistake. There is no Clausilia nigricans 

 in Dr. Pulteney's original work."^ In the 1892 list published by this 

 Society there appears Clausilia perversa {'?u\t.)=rugosa Drap. and 

 var. dubia Drap. is introduced under that species. This was the 

 name generally accepted at that time for the larger shell found so 

 commonly in the Craven district of Yorkshire and among the West- 

 morland Fells, on the assumption that it was identical with the 

 continental form. The list published in 1903 gives bidentata (Strom) 

 S^^:=perversa Pult. = rugosa Drap.]. Later on the var, cravenensis 

 Taylor was instituted, thus establishing the distinction from the 

 continental dubia. The general feeling to-day is that this form is 

 entitled to full specific rank. 



All three species or forms differ in the clausium, but it is my pur- 

 pose in these notes only to shew the distinction between dubia and 

 cravenensis. 



In a paper read before the Society in January, 1912/ Mr. H. 

 Overton expresses an opinion that dubia and cravenensis are idfentical, 

 and says he fails to discover any difference whatever. Thus his note 

 recording the occurrence of C. dubia at Dover becomes puzzling and 

 it was only quite recently that it occurred to me that the Dover shell 

 might not be, after all, identical with the Craven form. I wrote to 



1 Not apparently identical with Draparnaud's figure and description. 



2 British L. {^ F. W. Moll, Lovell Reeve. 



3 Journal 0/ Conch., vol. 13, p. 276. 



