124 Mr. W. Thompson's Catalogue of the Land and 



6. Planorbis umbilicatus, Mull. Jeffreys, Linn. Trans, v. 16. p. 384. 



P. marginatus, Drap. p. 45. pi. 2. f. 11, 12, 15 ; Gray, Man. p. 

 265. pi. 8. f. 87, 88, 90; Turt. Man. f. 87. 

 This species prevails in every quarter of the island, but is not ge- 

 nerally distributed. Attached to stones at Ram's Island, Lough 

 Neagh, I find a small variety f, about half the ordinary size, and 

 which is concave beneath, with the keel obscure — Mr. Alder re- 

 marked on some of these which I had the pleasure of adding to his 

 collection in 1835 — " Turton's P. rhombceus, of which he sent me 

 specimens, is the same thing in a younger state." Mr. Jeffreys, in 

 a letter dated Oct. 2, 1838, when acknowledging the receipt of the 

 Lough Neagh shell, observed that he considered it distinct from P. 

 marginatus, and that from a similar shell previously found at Cardiff, 

 he had named the form P. incequalis. It is to a distorted individual 

 of the P. marginatus, found in a pond at the College Botanic Garden, 

 Dublin, that Capt. Brown applied the name of Helix cochlea (Irish 

 Test. p. 528. pi. 24. f. 10.), andTurton that of Helix terebra (Conch. 

 Diet. p. 62. f. 55.) — Mr. O'Kelly, to whom the shell belongs, always 

 considered it P. marginatus, and as such noticed it in the Dublin 

 edition of Pennant's Brit. Zool., p. 363. The Rev. T. Hincks writes 

 me from Cork that " the var. of Plan, marginatus with the volutions 

 elevated into a spiral cone was once taken in Ballypheane bog." I 

 have myself met with monstrous forms of several of the native spe- 

 cies of Planorbis. 



7. Planorbis vortex, Mull. Gray, Man. p. 267. pi. 8. f. 91 ; Turt. 



Man. p. 109. f. 91 ; Drap. p. 44. pi. 2. f. 4, 5. 

 Helix vortex, Mont. p. 454. t. 25. f. 3. 



8. Planorbis spirorbis, Mull. Gray, Man. p. 268. pi. 8. f. 98; Turt. 



Man. p. 115. f. 98. 

 P. vortex, /3. Drap. p. 45. pi. 2. f. 6, 7. 

 Helix spirorbis, Mont. p. 455. t. 25. f. 2. 



The species which my correspondents (chiefly j udging from the 

 descriptions and figures in Turton's Manual) have considered as the 

 P. vortex and P. spirorbis, are noted as generally common in Ireland 



these shells merge so into each other that I was in the habit of 



putting all that were collected throughout the north together. On 

 comparing these with examples of " P. spirorbis" from the neigh- 

 bourhood of Newcastle, and of "P. vortex" from that of London, 

 presented me by Mr. Alder, I find that although some of them are 

 as large as the P. vortex, have seven volutions, and a carinated 

 edge to the lower one, that they are not of the extreme form desig- 

 nated by this name, and consequently come under P. spirorbis ; so 

 likewise do a number of specimens from the neighbourhood of 

 Portarlington sent me by the Rev. B. J. Clarke — those from the 

 river Shannon, favoured me by the Rev. C. Mayne of Killaloe, may 



f The size is, I conceive, attributable to the coldness of the water and 

 scarcity of subaquatic plants. 



