15 t08 Proceedings of the Royal Irish Academy, 



uncovered during low -tide, and have uol been uoted in pools; thus, bhougb 

 Bwepl with a considerable amounl of brackish water on the ebb-tide, its 

 habitat differs considerably from thai « > t" 1 1 1 1 - Last species, li is uol abundant, 

 but has been found, with the exception of the February visit, each time the 

 Looalit it's have been searched. 



When young, the plants are more or less orbicular, but Boon become 

 deeply divided and verj irregular. They occur in small clusters and are ol 

 medium size, an average specimen being 10-12 cm. in length; a few large] 

 fronds were found floating in pools; but it was not quite certain if thc\ 

 were detached from this species or from M. orbicularis. The thallus is usually 

 about 30 fx thick; and, unless growing in deep shade, is of a very pale colour 

 (of. No. 91). 



The agreement with M. crepidinum is, in deeply-cul angular specimens, 

 fairly close; but, in others, it is less marked, the fronds being large and 

 irregular. The American specimens in the Kew Herbarium, adhere very 

 tightly to paper, which is not the case with any of the Clew Bay material. 

 The lobed fronds appear to separate it from being a marine form of 

 M. orbicularis. 



Enteromorpha paradoxa var. tenuissima (Kiitz.), Batt. 



A few specimens of this beautiful species were found washed ashore at 

 < )ld Head (August, 1911). Though in poor condition, they are without doubt 

 referable to the plant mimed E. Hopldrkii by AlcCalla. The small chromato- 

 phores, and the monosiphonous ultimate ramulae, separate it from the majority 

 of the richly-branched species; and its extreme delicacy distinguishes it from 

 A'. , recta Hook. The plant has suffered much at the hands of systematists, 

 and its position will probably continue uncertain till the genus is thoroughly 

 revised. 1 have followed Batters (without investigating the point) who has 

 united it with Kiitzing's E. temtdssima, which he regards as a variety of that 

 author's E. i>tir<i<l<nu. 



Ulva Lactuca L. 



For recent work on the biology and ecology of Ulva, and especially its 

 growth in polluted waters, see Keports to the Sewage Commission (Letts and 

 Kichards '11; Cotton '11/;). An account of the structure of the basal disk 

 has also been published recently by Miss Delf (12). 



In the pure waters of Clare Island the plant is one of the most abundant 

 species in the more sheltered rock-pools during summer and autumn. It 

 is frequent on rocks also at Portlea ami at Old Bead; but in none of these 

 localities does Li attain a greal size. Large specimens may be dredged in 



