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ON THE BRITISH SPECIES Of TBUNCATELLINA. 



By A. S. Kennard, F.G.S., and B. B. Woodward, F.L.S. 



Bead 11th May, 1923. 



Doubt having been expressed in some quarters as to the validity 

 of Dr. Pilsbry's conclusion {Man. Conch., ser. ii, vol. xxvi, pp. 65 

 and 77) that two species of Truncatellina are present in Britain, and 

 neither of them identifiable with the inadequately described Pupa 

 minutissima of Hartmann, it became necessary for us in furtherance 

 of our special study of the Post-Pliocene Non-Marine MoUusca to 

 investigate the matter and, in the event of there being two species, 

 to ascertain what microscopic characters there might be which 

 would enable anyone to identify incomplete examples such as only 

 too frequently are the sole available material when dealing with 

 fossil occurrences. 



For valuable help in our investigations by loan of specimens we 

 have to thank Dr. A. E. Boycott, J. E. Cooper, A. Hartley, J. W. 

 Jackson (Manchester Museum), J. R. B. Masefield, C. Oldham, 

 A. E. Sahsbury, C. D. Sherborn, J. R. le B. Tomlin, and W. J. 

 Wintle. 



Our researches have been, we consider, entirely successful, and 

 the following tabular statement will show that there are two species 

 distinguishable from each other by well-marked and fundamental 

 characters, viz. T. cylindrica, Ferussac, and T. hritannica, Pilsbry. 



Cylindrica. 

 The same, but the outline of 



Shell. 



Whorls. 



Aperture. 



Britannic A. 

 Minute dome-topped cylinder. 

 The outline of the cylindrical 



portion showing practically 



parallel sides. 



Long. 1-6 to 1-85 ; lat. 0-8 to 

 (exceptionally) 0-9 mm. 



5^ (exceptionally 6). 



Nepionic shell smooth, IJ 

 whorls, sharply defined from 

 the succeeding whorls. 



Last three whorls flattened 

 convex, with well-defined 

 sutures. 



Strongly ribbed : the riblets 

 2 to 0-1 mm., crossing the 

 whorl at a high angle. 



Ovate, tending towards squar- 

 rose. 



Peristome whitish, somewhat 

 thickened and expanded, 

 especially in very old in- 

 dividuals. 



the cylindrical portion is 

 very slightly arcuate, like 

 the shaft of a well-formed 

 column. 

 Long. 1-8 to 2 ; lat. 0-9 mm. 



5i to 6. 



Nepionic shell smooth, IJ to 

 2 whorls, not always 

 sharply defined from the 

 succeeding whorls. 



Last three whorls convex, 

 with even more strongly 

 marked sutures. 



Less strongly ribbed : the 

 riblets 3 to 0-1 mm., 

 crossing the whorl obliquely 

 at a somewhat lower 

 angle. 



Ovate, tending slightly to- 

 wards triangular. 



Peristome very similar, but 

 the margin of the outer lip 

 is inclined towards the 

 columella as it descends 



