148 BRITISH MOLLUSKS. 



11. Planorbis nitidus. Shining Planorbis. 



Shell ; depressed, semitransparent amber liorny, upper disk with 

 the spire a little immersed, lower disk convexly 

 flattened with a rather narrow sunken umbilicus, 

 whorls three and a half to four, convexly sloping 

 on the upper part towards the periphery which 

 is obtusely angled, last whorl marked with a few 

 distant radiating lines indicating internal septa. 



Panorbis nitidus, Miiller (1774), Verm. Hist, part ii. p. 163 

 (not of Forbes and Hanley, nor Jeffreys). 



Helix lineata, Walker (1784), Test. Minut. Ear. p. 8. pi. i. 

 f. 28. 



Nautilus lacustris, Lightfoot (1786), Phil. Trans. PLoy. Soc. vol. lxxvi. 

 p. 163. pi. i. f. 1 to 7. 



Helix nitida, Ghnelin (1788), Syst. Nat. p. 3624. 



Planorbis complanatus, Poiret (1801), Prod. p. 93. 



Planorbis clausidatus, Ferussac (1820), Journ. Phys. p. 240. 



Planorbis nautilus, Sturm (1823), P>eutsch. Faun. vol. vi. pi. xv. 



Segmentina lineata, Fleming (1828), Brit. Anim. p. 279. 



Segmentina nitida, Fleming (1830), Edin. Encyc. vol. xii. 



Hemithalamus lacustris, Leach (1831), Turt. Man. p. 137. 



Segmentaria lacustris, Swainson (1840), Treat. Malac. p. 338. 



Planorbis (Segmentina) nitidus, Moquin-Tandon (1855), vol. ii. p. 424. 

 pi. xxx. f. 5 to 9- 



Hab. Central and (perhaps) Northern Europe. Chiefly in south of Eng- 

 land ; rare in Scotland and Ireland. (In ponds and ditches, on duck- 

 weed and other water-plants.) 



The shell of this species is distinguished in a very characteristic 

 manner by the presence of three or four septa within the last whorl, 

 and when seen externally they give the whorl an appearance of 

 being radiately divided into segments. They were described by 

 Midler, the founder of the species, as " streaks like ligaments," 

 which he supposed to be the repairs of fractures. Mr. Jeffreys con- 

 siders them as being somewhat analogous to the parietal teeth of 

 Pupa and Vertigo, which is not improbable. The shell of P. niti- 

 dus is rather larger and duller in aspect than that of the preceding 

 species, and the whorls do not slope into so prominent an angle at 

 the periphery, whilst they are more flattened around the umbilicus, 

 which is smaller. 



It has been observed that Planorbis nitidus is rather more active 

 in its movements than others of the genus, and carries its shell 



