r. 



Rev. W. Smith on Deposits of Diatomaceous Earth. 121 



description nor Wood^s figure answers to my insect, 1 will^add the 

 characters of this species, which was unknown until I took three 

 flying near the ground by a 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 tibise tawny, the latter 

 tipped fuscous ; anterior tibise 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 tibise. 



18, Belitha Villas, Barasbury Park, 1st 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. Smith, F.L.S. 



During 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 DiatomacecB. 

 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 exuvise, and understanding from Mr. 

 M'Adam that the determination of the point 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. 



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 



