O’Mrara—Report on the Irish Diatomacee. 265 
Coscinodiscus minor, (Ehr.) Marine. 
Disk small. Cellules roundish, without any perceptible arrange- 
ment. (Pl. 26, fig. 25.) 
Ebr, Mic.;! T. xviii fig (815) Dxx:-i.) fig..28; ‘Ti xxim, fig::27 ; 
T. xix., fig. 3. Kiitz. Bac., p. 131, T.i., figs. 12, 13. Ralfs, in 
Pritch., p.831. Weisse, Recherches Microscopiques sur le Guano, Bul. 
de ]’Academie Imperial de Science de St. Petersburg, T. xu, p. 121, 
Piti., fige22: 
Tide-pool, Dalkey, Co. Dublin. 
Coscinodiscus punctulatus, (Greg.) Marine. | 
Striz 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, 
but all mountedin 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 Ralfs, as 
to whether the form is properly referred to the genus Coscinodiscus. 
Gregory, Diat. of Clyde, p. 28, Pl. x., fig. 46. Ralfs, in Pritch., 
p- 881. 
Arran Islands. From stomachs of Ascidians, Roundstone Bay, 
€o. Galway. On Fucus serratus, Ballybrack, Co. Dublin. 
Genus VII. Aracunorpiscus, Ehr. Deane. 
Arachnoidiscus Ehrenbergii, (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.’’—Ralfs. 
Wim om, B.)). Vol. ip: 20; Supp. Pl. xxx,;.fie; 256: Ralfs, 
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. Rabenhorst does not give it a place among the European 
species of Diatomacez; and perhaps he wasrightin excluding it. But 
it seems desirable to notice the fact of its having been found. Besides 
