Rey. W. Smith on Deposits of Diatomaceous Earth. 121 
description nor Wood’s figure answers to my insect, I will’add the 
characters of this species, which was unknown until I took three 
flying near the ground bya hedge at Niton, in the Isle of Wight, 
the 30th of July 1828. 
It expands 1 inch and is yellowish-white : the superior wings 
are more or less freckled, deeply cleft, the upper lobe narrow and 
curved, the costa and inferior margins are tawny, forming an 
oblique line towards the extremity composed of two trigonate 
spots, that on the costa being the larger: inferior wings yellow- 
fuscous, divided into three rays, without any lobe on the abdo- 
minal one: legs white ; thighs and hinder tibiz tawny, the latter 
~ tipped fuscous ; anterior tibiz clavate and brown, except at the 
base, intermediate clubbed or tasseled with brown scales at the 
apex, and another similar tassel at the middle. 
P. similidactylus varies in colour greatly, for one of my speci- 
mens is of an uniform dove-colour, except the darker markings 
on the upper wings, and the white but spotted legs. It is distin- 
guished from the allied species by the narrow upper lobe of the 
superior wings and the tasseled spotted tibiee. 
18, Belitha Villas, Barnsbury Park, lst Jan. 1850. 
XIV.—On Deposits of Diatomaceous Earth, found on the shores 
of Lough Mourne, County Antrim, with a record of species 
living in the waters of the Lake. By the Rev. W. Smiru, F.L.S. 
Durine a late visit to the North of Ireland I had placed in my 
hands, by Mr. J. M‘Adam of Belfast, a small quantity of earth 
which from its peculiar appearance he fancied might contain the 
shells of “Infusoria.” <A very slight examination convinced me 
of the correctness of this conjecture, and proved that the entire 
substance of the earth in question consisted of a mass of un- 
broken or fragmental siliceous shells of various Diatomacee. 
Being desirous of ascertaining the exact nature of the deposit 
from which the earth had been procured, and how far it had 
claims to the character of “ fossil,” a term which has frequently, 
but I fear without sufficient consideration, been given to similar 
collections of these beautiful exuvize, and understanding from Mr. 
M‘Adam that the determination of the poimt would be of some 
importance as regarded a paper on the Geology of the district 
which he hoped in a short time to prepare for the ‘ Annals,’ I 
determined to visit the spot, and record the particulars required 
from personal observation. F 
Lough Mourne is a sheet of fresh water of about two miles in 
circumference, lying amidst a range of low hills to the north-east 
of the town of Carrickfergus, at the distance of four miles from 
