90 



lighter colour underneath, finely and rather distinctly marked 

 with black specks : tentacles long, slender, bluntly pointed : 

 foot acutely rounded in front and obtusely so behind. 



SHELL compressed, concave above and flat or very slightly 

 convex below, rather thin and glossy, yellowish-horncolour, 

 finely and closely striate in the line of growth, with a few 

 slight spiral striae : epidermis thin : periphery strongly keeled 

 towards the middle : whorls 5-6, the diameter of the last 

 being rather less than a third of the whole spire, moderately 

 convex above, but much less so beneath, sloping gradually 

 on both sides to the periphery : suture deep : mouth obliquely 

 oval, sharply angulated above, the inside sometimes thick- 

 ened : outer lip slightly reflected : inner lip continuous with 

 it, much spread on the columella : umbilicus very indistinct, 

 owing to the lower side being nearly flat. L. 0*1. B. 0*5. 



Var. disciformis. Shell flatter and thinner, of a yellowish 

 colour, having the last whorl larger in proportion to the 

 others, and the keel more prominent and sharp and placed 

 exactly in the middle. P. lutescens (afterwards altered to 

 disciformis}, Jeffr. in Linn. Tr. xvi. pp. 385 & 521. 



HABITAT : Marshes and stagnant water in our home 

 and eastern counties, as well as in those of Dorset, Somer- 

 set, Northampton, York, Glamorgan, and many parts of 

 Ireland. Dr. Leach says that it also occurs near Edin- 

 burgh. It is, however, local, and never plentiful. It is 

 an upper tertiary fossil. The variety is found in Bucks, 

 Oxford, Cambridge, Glamorgan, Cork, and Tipperary, and 

 is somewhat rare. This variety bears the same relation 

 to the typical form as the P. compressus of Michaud does 

 to P. vortex. The monstrosity, so common in this genus, 

 in which the last whorl is disjoined from the rest, also 

 occurs, but very seldom. It is a Swedish species, and 

 ranges southward to Portugal and Corsica. 



This mollusk is very slow in its movements, but ap- 

 pears to be fond of floating. It lays from 10 to 20 eggs, 

 which quit the capsule in from ten to fifteen days. It is 

 occasionally met with in company with the next species. 



