IRISH AND ENGLISH OSTRACODA. J 05 



2. In the upper bed — 



Cypris reptans (Baird). 



— gibba, Ramdohr. 

 Cypridopsis obesa, Brady and Robertson. 

 Candona detecta (Miiller). 



7. Cardiff — New Dock Basin. 



This deposit is of an estuarine character, becoming more marine in its lower portions. 

 We examined separately portions of the clay taken from eight, fifteen, twenty, thirty, 

 and forty feet below the surface. It varies little in composition, although it alters in 

 colour from brownish to dark grey, but at the depth of forty feet it alternates with 

 beds of gravel to the depth of sixty-four feet, where it reaches a red marl. 



At eight feet below the surface the dry clay consists of 96 per cent, fine mud, 4 per 

 cent, shell debris and fine sand. 



At forty feet, 94 per cent, fine mud, 6 per cent, fine and coarse sand, with a few 

 fragments of shells and a small portion of vegetable matter. The deposit contains some 

 freshwater and brackish, as well as marine, forms, — a fact accounted for by its position at 

 the mouth of the River Tafi". 



The prevailing species is Scrobicularia piperata, the characteristic shell of the 

 Mersey and the Montrose estuarine muds. It ranges from top to bottom of the clay, 

 and, in some places, lies in bands with little admixture of clay. 



Although the whole fauna has an estuarine character, it is more diversified and more 

 decidedly marine towards the bottom. The alternations, however, are so capricious 

 that no lines of regular change can be drawn in the fauna. For example, at forty feet 

 below the surface Cytliere porcellanea prevails over Cythere castanea ; at fifteen feet 

 C. castanea prevails over C. porcellanea ; at eight feet C. porcellanea prevails over 

 C. castanea. 



At the depth of forty feet the shells of Ostracoda and those of young Mollusca 

 are filled with iron -pyrites. This is also the case at eight feet below the surface ; 

 but at the intermediate depths of fifteen, twenty, and thirty feet scarcely a trace of it 

 is seen. 



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