140 The Irish NaU^raUst. 



Plcdonema terebrans^ an extremely delicate form, can onlj^ 

 be observed after decalcification and subsequent examination, 

 as it gives no external indication of its presence. Threads of 

 it are frequently found in preparations of other algae, from 

 which it is at once distinguished by its long slender segmented 

 filaments, much interwoven with each other. 



The red alga, Conchocelis rosea, first observed by Batters in 

 1892, stains pink, so its presence can be at once determined : 

 tests being employed to make sure we are looking at a shell- 

 borer. The filaments swell out into irregularly-shaped in- 

 flations, more or less constricted at the joints. In the centre 

 of each cell of the inflations there is a star-shaped chroma- 

 tophore. 



The shell-destroyers, which are looked upon by Bornet as 

 belonging to the colourless group of Fungi, are Ostraeoblabe 

 and Lithopythiufn. The latter has not 3'et been recorded from 

 this country. 



A marine lichen named Verriicaria consequens was, in 1894, 

 obtained in shells collected at Bundoran b}^ Professor Johnson. 

 It will perhaps not be out of place here to explain what we 

 understand by the term lichen. Lichens are compound bodies 

 consisting of two organisms — a fungus and an alga, variously 

 associated. The fungus absorbs the required water and 

 mineral substances ; the algal portion of the lichen, possessing 

 chlorophjdl, absorbs carbonic dioxide, evolves ox3'gen, and 

 forms starch, &c., thus supplying the organic food necessary 

 for the nourishment of the whole plant. We have in this 

 wa3^ a case of division of labour among organically distinct 

 plants, to form a S3anbiotic organism, with marked peculiarities 

 of its own. The fruit of a lichen, which is ahvays formed 

 entirely of the fungal element, ma3' be open and cup-like 

 (apothecium), or enclosed in a cellular covering (peri- 

 thecium). Verrucai'ia consequens has long been known from 

 the west of Ireland, but M. C Bommer was the first to show, 

 in 1892, its perforating powers in Belgian specimens. It was 

 first noticed in limpet-shells ; later on it was observed in 

 Purpura and acorn barnacles. 



On looking at an3^ shells attacked b3^ this lichen, we notice 

 dark spots as indentations scattered over the surface, the 

 perithecial fruits of the lichen, formed from the fungal 



