64 LIMNJEADJE. 



This pretty little shell cannot possibly be confounded 

 with any of the other species of Planorbis. Its whorls 

 are six in number, and extremely narrow, but promi- 

 nent and well defined. Diameter about one-fifth of an 

 inch, height one tenth. The mouth is peculiarly small 

 and unarmed. Aperture of a narrow crescent shape, 

 only slightly produced on the upper side. 



Hob. Widely distributed throughout the British 

 Isles, though absent in some districts. It may generally 

 be found in ponds, ditches, or slow streams. 



P. NITIDUS. Mutter. PI. VII, fig. 22. 



Shell depressed, smooth, polished, transparent, horn coloured, cari- 

 nated at the periphery, flat above, concave beneath, wrinkled. 



Helix fontana, Light. Planorbis complanatus, Drap. 



This shell, which is by no means common, closely 

 resembles the succeeding species, but is more depresed, 

 less polished, pale coloured, and devoid of septa. 

 Whorls more convex and distinct and rather wrinkled ; 

 umbilicus much larger. The shell is seldom a quarter 

 of an inch in diameter. 



Hob. Though this species is not mentioned in the 

 fauna of several districts, there is reason to believe it is 

 generally distributed through England. We have met 

 with it, but sparingly, in several localities in Yorkshire, 

 in clear stagnant water on acquatic plants. 



P. LACUSTRIS. Lightfoot. PI. VII, fig. 25. 



Shell highly polished, with internal partitions ; whorls flattened ; 

 periphery carinated ; aperture triangular. 



Planorbis nitidus, Mull. Sementina lineata, Flem., 

 Gray. 



This beautiful Planorlis is about a quarter of an 

 inch in diameter, and remarkably smooth, shining, and 

 transparent, of an olivaceous brown colour, with white 

 radiations on the outer volution, exhibiting the internal 

 partitions. The upper side is flattened convex, having 

 the middle whorls of the spire thick ; the under side 



