82 LIMNvEID^. 



Corsica. Although it is much less local than the last spe- 

 cies^ I am not aware of their having been found together. 



Its habits are slower and more timid than those of P. 

 lineahis ; and it is not so fertile, never laying more than 6 

 eggs. The shell is often infested by the minute egg-cases 

 of a water-insect, or coated with the spores of Confervce. 



The shell differs chiefly from that of the last species in 

 being of a lighter colour, flatter, and thinner, in the 

 whorls being more visible above, the keel being much 

 sharper, and especially in the absence of the internal 

 septa or partitions. 



B. Whoi'ls few. 



3. P. Nauti'leus"^, Linne. 



Tm^bo Nautileus, Linn. Syst. Nat. ed. xii. p. 1241. P. Nautileus, F. & H. 

 iv. p. 152, pi. cxxyi. f. G, 7. 



Body greyish- brown, with sometimes a faint reddish tinge, 

 minutely speclded with black : head very large and thick : 

 tentacles long and cylindrical, greatly diverging : eyes distinct, 

 scarcely prominent : foot broad, rounded in front, and ending 

 in a blunt point behind. 



Shell quoit-shaped, having the upper side flat and the 

 lower side rather convex, thin, not glossy, light-brown or grey, 

 sometimes white, closely striate by the lines of growth, which 

 at distant but regular intervals form strong curved ridges and 

 frequently rise into projections like the rowels of a spiu* on the 

 outside : epidermis rather thick : periphery bluntly and in- 

 distinctly keeled : whorls 3, depressed above, the last exceed- 

 ing in size the rest of the shell : suture rather deep : mouth 

 oblique, and either oval or nearly circular, according to the 

 greater or less depression of the whorls : outer Up thin, form- 

 ing with the inner lip in the adult a complete peristome : iim- 

 hilicus very large and exposing all the spire. L. 0*035. B. 0-1. 



Var. cristata. Shell having the transverse ridges stronger, 

 and the periphery deeply notched or crested by them. P. cris- 

 tatusy Drap. Hist. Moll. p. 44, pi. ii. f. 1-3. 



* Shaped like a Nautilus. 



