308 
MOLLUSCA. 
Cork ; near this city the “ P. planatus ” is noticed by Mr. Humphreys as 
met with. Mr. Alder and Mr. Forbes consider the Lough Derg shell P. 
carinatus, and, according to the former, it is the P. disciformis, Jeff. 
P. umbilicatus , Mull. 
This species prevails in every quarter of the island, but is not generally 
distributed. Finnoe, County Tipperary, Mr. Waller. Attached to stones 
at Ham’s Island, Lough Neagh, I find a small variety, about half the or- 
dinary size, and which is concave beneath, with the keel obscure. Mr. 
Alder remarked on some of these which I had the pleasure of adding to 
his collection in 1835 — “ Turton’s P. rliombceus, of which he sent me spe- 
cimens, 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 ap- 
plied the name of Helix cochlea (Irish Test., p. 528, pi. 24, f. 10), and 
Turton 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 Bally- 
pheane bog.” I have myself met with monstrous forms of several of the 
native species of Planorbis. 
P. vortex, Mull.' 
Generally distributed. 
P. spirorbis, Mull. 
The species which my correspondents (chiefly judging from the de- 
scriptions 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 neighbourhood 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 volu- 
tions, and a carinated edge to the lower one, that they are not of the ex- 
treme form designated 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 be placed 
under P. vortex , as may those also collected at Lough Gounagh, County 
Longford, by my friend R. Callwell, Esq., of Dublin. Is the more promi- 
nent keel, with other differences necessarily attendant on it, as form of 
mouth, &c., sufficient for specific distinction between P. vortex and P. 
spirorbis f Under Planorbis disciformis, Mr. Alder has well remarked, 
that “ the degree of carination is so very variable in different individuals 
of the same species, that it is rather fallacious as a distinguishing charac- 
ter.” — Mag. Zool. and Pot., vol. ii. p. 113. 
Specimens of P. compressus, Michaud, from Lorraine, with which I 
have been favoured by their describer, are identical with those of P. vor- 
tex before noticed as from Mr. Alder. Examples of P. leucostoma, 
