98 



nearly the same reasons, called the present species Plan- 

 orbis turritus. But the Linnean epithets "spira pro- 

 minente" and "spira obsoleta" appear unmistakeably 

 to distinguish the two species ; and, at all events, it 

 would now be very inconvenient to make any change of 

 name by adopting that given by Muller, instead of the 

 one by which this species is so universally known. The 

 late Dr. Fleming proposed to separate it generically from 

 the next under the name of Aplexa ; but this separation 

 has only been adopted by a very few conchologists. A 

 well-known European species, P. acuta, seems to con- 

 nect the two British forms, both as regards the soft parts 

 of the animal and the shell. 



B. Mantle having lobes or digitated processes which expand 

 over the shell ; the latter being destitute of an epidermis 

 and having a short spire. 



2. P. FONTINA'LIS*, Linne. 



Bulla fontinalift, Linn. Syst. Nat. ed. xii. p. 1185. P. fontinalis, 

 F. & H. iv. p. 140, pi. cxxii. f. 8, 9. 



BODY lustrous, dark grey with sometimes a slight tint of 

 yellow or violet : mantle fringed with about a dozen lobes 

 or digitations of unequal size : tentacles rather slender, light 

 grey : eyes conspicuous : foot obtusely rounded in front, and 

 contracted behind to a somewhat fine point. 



SHELL oval, extremely thin, glossy, semitransparent, grey- 

 ish-horncolour with a slight tinge of yellow or brown, faintly 

 striate by the lines of growth and microscopically striate in 

 a spiral direction : whorls 4-5, swollen, the last occupying 

 considerably more than three-fourths of the shell : spire not 

 much produced, blunt at its point : suture moderately deep : 

 mouth nearly of the same form as that of the preceding spe- 

 cies, but much larger and wider in proportion : outer lip very 

 thin and flexuous : inner lip much spread on the columella, 

 which has a slight and narrow fold on its lower side. L. 

 0-35. B. 0-25. 



* Frequenting fountains. 



