O'Meara — Itejjorf on the Irish Diatomacece. 265 



Coscmodiscus minor, (Ehr.) Marine. 



Disk small. Cellules roundish, without any perceptible arrange- 

 ment. (PI. 26, fig. 25.) 



Ehr. Mic., T. xviii., fig. 31 ; T. xx.-i., fig. 28 ; T. xxii., fig. 27 ; 

 T. xix., fig. 3. Kiitz. Bac., p. 131, T. i., figs. 12, 13. Ealfs, in 

 Pritch., p. 831 . "Weisse, E-echerches Microscopiques sur le Guano, Bui. 

 de I'Academie Imperial de Science de St. Petersburg, T. xii., p. 121, 

 PL i., fig. 22. 



Tide-pool, Dalkey, Co. Dublin, 



Coscinodiscus punctulatus, (Greg.) Marine. 



Striae indistinct. Disk covered with what appear to be fine puncta, 

 irregularly scattered. 



Gregory describes the disk in his specimens as " marked by very 

 fine and obscure lines, which, near the margin, are traceable as rays, 

 but which soon become fainter, and apparently wavy, at the same 

 time as they proceed towards the centre." — Diat. of Clyde, p. 28. 



Several specimens, from different localities, came under my notice, 

 hut all mounted in balsam. In consequence I could not trace the lines 

 referred to ; and, moreover, the puncta in such forms as were seen 

 •obliquely had the appearance of fine hairs. This circumstance increases 

 the doubt which I entertain, in common with Gregory and Ealfs, as 

 to whether the form is properly referred to the genus Coscinodiscus. 



Gregory, Diat. of Clyde, p. 28, PL x., fig. 46. EaKs, in Pritch., 

 p. 831. 



Arran Islands. From stomachs of Ascidians, Eoundstone Bay, 

 €o. Galway. On Eucus serratus, Ballybrack, Co. Dublin. 



Genus YII. AEACHNOiDiscrs, Ehr. Deane. 



Arachioidiscus Ehrenlergii, (Bailey.) Marine. 



"Disk with a central hyaline nodule or umbilicus, and numerous 

 radiating lines, connected by concentric circles of large pearly granules ; 

 the circle next the umbilicus formed of short lines." — Ealfs. 



Wm. Sm., B. D., Vol. i., p. 25 ; Supp. PL xxxi., fig. 256. Ealfs, 

 in Pritch., p. 842, PL xv., figs. 18-21. 



This truly splendid form has been discovered in the fossil earths of 

 California, and in a living state it has been gathered in Japan, Cali- 

 fornia, and South Africa. It is its habit in congenial climates to cover 

 completely the plants to which it is attached. It admits of serious 

 doubt, therefore, whether the few isolated specimens which have been 

 discovered in this kingdom entitle it to be included among our British 

 forms. . Eabenhorst does not give it a place among the European 

 species of Diatomacea^ ; and perhaps he was right in excluding it. But 

 it seems desirable to notice the fact of its having been found. Besides 



