PLANORBIS. 81 



made known by Mr. Walker, an intelligent bookseller at 

 Faversliam in Kent, tbe description of it having been 

 supplied to bim by Mr. Jacob. The only share which 

 Mr. Boys appears to have had in the discovery is his 

 having sent parcels of shell-sand to Walker; but the credit 

 of the publication entirely belongs to the latter. Two 

 years afterwards Lightfoot described and published this 

 species in the ^Philosophical Transactions/ under the 

 name of Nautilus lacustris. 



2. P. n/tidus*, Miiller. 



P. nitidus, Miill. Verm. Hist. pt. ii. p. 163 ; F. & H. iv. p. 161, pi. cxxvii. 

 f.11,12. 



Body reddish-grey, with sometimes a yellowish tinge, and 

 marked with extremely fine dark-grey specks : tentacles very 

 long and slender : eyes rather large : foot short, very broad in 

 front, and sHghtly narrowing behind to an abrupt but not a 

 fine point. 



Shell shaped like the last, but flatter and with much more 

 of the spire visible above, in consequence of the last whorl 

 not clasping such a large part of the preceding one, very thin, 

 glossy and prismatic, hght-j^ellowish-horncolour or grey, with 

 sometimes a reddish tinge, faintly striate by the lines of growth, 

 with occasionally a few spiral microscopical hues, which are 

 more distinct on the under side, giving an appearance of the 

 sculptui'e pecuhar to the shells of Limncea : epidermis ex- 

 tremely dehcate : periphery rather sharply keeled : whorls 4-5, 

 the last covering about one -half of the preceding whorl : su- 

 ture rather deep : mouth and outer lip formed as in P. lineatus, 

 but larger : umbilicus small, not deep. L. 0-06. B. 0*225. 



Habitat: Ponds, marshes, and stagnant water through- 

 out Great Britain, from the Moray Firth district south- 

 wards. It is also one of our upper tertiary fossils. 

 MiddendorflP has included it in his list of Siberian shells ; 

 and it is extensively distributed over the European con- 

 tinent, having apparently its most southern limit in 



* Shining. 



E 5 



