PLANORBIS. 85 



The description of its colour (" alba''), as well as all the 

 other characters given of this species in the ' Fanna 

 Suecica/ are peculiarly appropriate to P. albus. The 

 present species being common in Sweden, and not likely 

 to be confounded with any other, could scarcely have 

 escaped the keen observation of the great naturalist; 

 and it was not otherwise noticed by him. However, as 

 the confusion has already been too great in the specific 

 names of this genus, I will not venture to increase it by 

 restoring Linne's name. 



5. P. gla'ber*, Jeffreys. 



P. glaber, Jetfr. in Linn. Tr. xvi. p. 387 ; F. & H. iv. p. 150, pi. cxxvi. f.8,9. 



Body yeUowish-grej : tentacles rather short, cylindrical, and 

 ending in a blunt point : foot rather broad, especially in front, 

 with a yellowish edge. 



Shell rather convex above and depressed in the centre, 

 concave below, rather thin, glossy and sometimes iridescent, 

 greyish-horncoloiu' aud occasionally marked with w^hite curved 

 streaks in the line of growth, finely but iiTCgularly striate 

 transversely, and very faintly and obscurely striate in the op- 

 posite or spiral direction ; the spiral stria3 are only visible in 

 some lights and by the aid of a strong magnifying power : 

 epidermis thin and smooth : ])eripJiery rounded : wliorls 5, con- 

 vex, but somewhat angular, the last scarcely exceeding one- 

 half of the shell : suture very deep : mouth rather more circular 

 than oval : outer lip slightly reflected, the upper edge project- 

 ing a httle beyond the lower one : inner lip united to the colu- 

 mella, but continuous with the outer Up : umbilicus large and 

 rather deep. L. 0-05. B. 0-15. 



Habitat : On aquatic plants in marshes, lakes, and 

 ponds, from Burra fiord in Unst to Penzance ; but it is 

 not generally difi'nsed. It is an upper tertiary fossil. I 

 only know of about twenty localities. The largest speci- 

 mens I have seen w^ere found by Mr. Bridgman near 



* Polished. 



