LAND AND FHESH WATER MOU,USKS, 57 



Planorbis albus, 3Ial. — Rather uncommon on the leaves of N. lutea, in 

 company with V. lacustris. 



Planorbis imbricatus, Mul. — Rare on Callitriche verna in a ditch near the 

 Ouse. 



Planorbis carinatus, Mul. — In stagnant ditches in the levels not very 

 general. 



Planorbis marginatus, Drap. — Very common. 



Planorbis vortex, Mai. — \ Both common perhaps, but I really am puzzled 

 Planorbis spirorbis, Miil. — •) to distinguish them. 



Planorbis nitidus, Mul. — Until last spring I had considered this species 

 very i*are, having only met with one or two specimens, and those by mere 

 chance, but on the 14th. of April last I dragged from a ditch in Kingston 

 brooks a quantity of Confervce, and on examining it, found some shells I had 

 often wished to find; I resolved therefore to carry some home in my vasculum, 

 and try an experiment recommended by a friend, namely, to place the mass 

 in a basin and pour some warm water on it. This answered admirably; the 

 animals relinquished their hold and fell to the bottom, and what was my 

 surprise to find, on straining the water away, not two or three, but some 

 dozens of various sizes, doubtless young ones; I was indeed much delighted 

 with this discovery. As observed by my friend, they appear to come to 

 maturity rapidly, for they all disappeared in about eight or ten days. 



Planorbis contortus, 3Iul. — Extremely common in ditches among Fresh- 

 water Algae. 



Segraentina lineata, Flein. — Rare; only two specimens have been noticed 

 as yet, but the probability is, by adopting the above mode, it will be found 

 comparatively common. 



Cyclostoma elegans, Drap. — Abundant in the hedges round the South 

 Downs. 



Cyclas cornea, Lam. — Very common. 



Cyclas lacustris, Tuii. — Rare: but few have been found in the Cuckmere 

 River. 



Pisidlum obtusale, Pfel. — Not common in clear ditches. 

 Pisidium pusillum? Gray. — Occasionally among Fresh-water Algae, with other 

 minute species. This genus requires some attention to distinguish the species; 

 I have oftentimes had my skill put to the test, and even then have not arrived 

 at a satisfactory decision. 



Pisidium Henslowianum, Jen. — Two specimens only. This species is easily 

 known, not only by its striking characters, but also by its size. 



Pisidium amnicum, Jen. — Rare: in the Cut and the streams which empty 

 themselves into the Ouse: not common. 



Anodon cygneus, Turt. — Common in the Ouse and its tributaries. I possess 

 a very fine specimen, given me by my friend Mr. Potter, which measures 

 eight inches in length, and four and a half in width, with a beautiful well- 

 marked and naturally-polished epidermis. It was taken, with several others 



