ANCYLUS. 121 



Dorset : very rare (J. G. J.). Var. 2. Sark ; Osmington 

 mills^ near Ringstead^ Dorset ; Dunboy, near Bearhaven, 

 Co. Cork (J. G. J.). This last variety is the A. deper- 

 ditus of Ziegler and Dupuy ; but (according to Bour- 

 guignat) not of Desmarest, who first used that name 

 for another species. Intermediate forms in respect of 

 the position of the beak incline me to consider this only 

 a variety. Var. 3. Wokey hole^ near Wells (Beevor) ; 

 Scarborough (Bean) ; near Torquay (Norman) ; Arish 

 mill^ near Lul worthy Dorset (J. G. J.). Specimens 

 from different places vary in colour from white to dark- 

 horncolour or reddish-brown. This species is also one 

 of our upper tertiary fossils. Abroad it ranges from 

 Finland to Algeria and Sicily ; and the Rev. R. T. Lowe 

 has incladed it in his list of Madeiran land-shells. 



M. Bouchard- Chantereaux published, nearly thirty 

 years ago, an extremely interesting account of the em- 

 bryogeny of A. fluviatilis, illustrated by a plate showing 

 the successive development of the spawn into the fry. 

 He says, each individual lays, in the course of the breed- 

 ing-season, about 80 eggs, which are enclosed in from 

 7 to 10 capsules and arrive at maturity in from twenty- 

 four to twenty-seven days, according to the temperature. 

 The animal seems to be more fond of Fontinalis antipy- 

 retica than of any other plant. 



Many species have been carved out of this variable 

 kind by Continental authors. In very young shells may 

 be detected faint traces of a more complete spire, which 

 is intorted so as to cause a concavity in the beak, called 

 by M. Bourguignat the " depression apicale.^^ This 

 species was first made known by Lister, and described 

 by him under the name of Patella fluviatilis, but ac- 

 companied by other epithets. It has by some authors 

 been considered to be the Patella lacustris of Linne ; 



G 



