PLANORBIS PRECURSOR. 33 



Dlsfribntioii. — Recent : in all parts of Great Britain ; abroad from Siberia and 

 Iceland to Morocco, Algeria and Sicily. 



Fossil: Butleyan Crag: Hollesley, Butley. Icenian — Norivich 

 zone : Bramerton, Beccles, Yarn Hill, Bulcliamp. Weyhourne zone : North 

 Walsham boring. Freshwater bed. West Runton. Pleistocene and Holocene 

 deposits of England, including Woodston, the Barnwell gravels, lacustrine beds 

 of Holderness, Selsey, etc. 



Pleistocene: France: Menchecourt, Hers (Haute Graronne). Germany: 

 Cannstadt, Weimar.^ Newer Holocene : Sweden and Denmark (Nordmann). 



Bemarl's. — -This species was known to Wood from Butley and Bulcliamp. It 

 has been found since at Hollesley and Yarn Hill, by Mr. Crowfoot at Beccles, 

 by Mr. Jas. Reeve at Bramerton, and by Mr. C. Reid at West Runton. Messrs. 

 Kennard and B. B. Woodward remark that it is a common Pleistocene fossil, its 

 earliest record on the Continent being from the Middle Pleistocene of Cannstadt 

 and Weimar. 



Planorbis praecursor, Kennard and B. B. Woodward. 



1848. Planorbis complanatus, S. V. Wood, Men. Crag Moll., pt. i, p. 9, tab. 1, fig. 10. 



1890. PIcmorbis complanntus, C. Reid, Plioc. Dep. Brit., p. 229. 



1899. Planorbis niarcjinatus, Kennard and B. B. Woodward, Proc. Malac. Soc, vol. iii, p. 197. 



1911. Planorbis precursor, Kennard and B. B. Woodward, G-eol. Mag. [5], vol. viii, p. 402. 



Specific Characters. — Shell sinistral, discoidal, smooth ; spire depressed, nearly 

 flat beneath ; margin slightly carinated ; aperture simj)le, lunate, sub-quadrate, 

 oblique ; outer lip thin ; inner lip slightly spreading over the body whorl (K. and 

 B. B. W.). 



Dimensions. — Diam. 12 mm. H. 2 mm. 



Distribution. — Not known living. 



Fossil : Butleyan Crag, Hollesley, Butley. Icenian : Bramerton, 

 Coltishall, Southwold, Bulchamp. 



BemarJcs. — As a rule the multiplication of new species and the alteration of a 

 well-established nomenclature are to be avoided, but it is sometimes desirable, 

 especially in the case of shells Avhose disappearance may have antedated the 

 appearance of the Recent species to which they have been affiliated. 



I adopt, therefore, the view taken by Messrs. Kennard and B. B. Woodward 

 that this and several other Crag mollusca dealt with above, though allied to the 

 Recent forms to which they have been hitherto referred, should be separated from 

 them. 



For the Crag shell described as P. complanatus, Linn. (S. V. Wood), and P. 

 marginatus, Drap. (K. and B. B. W.), they now propose the name F. prsecursor, 



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