270 Proreedings of the Roi/al Irish Acadenuj. 



Genus XIII. Aijliscus, Elir. 



Surface of the valve undulate, fumislied with two large processes; 

 striae plumose, arranged in form of a quatrefoil. 



AuUscus sculptiis, ("Wm. Sm.) Marine. 



StrijB linear. (PL 27, fig. 4. ) 



EaKs, in Pritch., p. 845, PL vi., fig. 3. Greville, Q.J.M.-S., 

 1863, p. 43, PL ii., figs. 1-3. Heiherg, De Danske Diat., p. 37. 

 Cleve, Om Svenska och Xorska Diat., p. 218. — Eupodiscus sculptus, 

 "Wm. Sm., B. D., Yol. i., p. 25, PL iv., fig. 42. — Aulacodiscus sculp- 

 tus, Brightwell, Q. J.M. S., 1860, p. 94, PL v., fig. 3. 



IkTalahide. Piles of wooden bridge, Dollymount, Co. Dublin. Hirer 

 Slaney, at Killui-in, Co. Wexford. Sea- weeds, near town of Wicklow. 

 "Westport, Co. Galway. 



Genus XIY. 0D0>'T0Discrs, Ehr. 

 Disk furnished with marginal teeth. 



In this genus I have united Ehi-enberg's two genera, Odontodiscus 

 and Systephania, deeming the distinction between them not of suffi- 

 cient importance to justify their separation. The distinction, as ex- 

 pressed by Ralfs, is simply this, that in Odontodiscus "the dots arc 

 radiate, not parallel, as in Systephania." 



Odontodiscus excentricus, (Ehr.) Harine, 



Disk varying in size from "0008 to '0025 ; areolate ; areoles round,^ 

 arranged in curved excentric lines; teeth numerous, short. (PL 27, 



fig. 5.) 



Ehr. Mic, T. xxxv., A. 18; fig. 11. RaUs, in Pritch., p. 832. 

 PL v., fig. 90. — Coscinodiscus excentricus, Kiitz. Bac, p. 131, T. i., 

 fig. 9, in which the teeth are not figured or described, "Wm. Sm., 

 B. D., Vol. i., p. 23, PL iii., fig. 38. — Eupodiscus excentricus, O'M., 

 a. J. M. S., 1867, p. 249, PL viL, fig. 2. 



Sea-weeds, Bannow. Salt ditch near "Wexford. Piles of wooden 

 bridge, Dollymount, Malahide, Stomachs of Pectens, Dalkey, from 

 Corallines, Howth, Sea-weeds, Ballybrack, Co. Dublin. Sea-weeds, 

 "Kilkee, Stomachs of Ascidians, Co. Clare. Stomachs of Ascidians, 

 Eoundstone Bay, Co. Galway. 



Odontodiscus ayiglicus, (Donkin.) Marine. 



Disk about '0016 in diameter ; teeth large and prominent, occupy- 

 ing a tolerably broad unstriate margin ; stiife minutely punctate, decus- 

 sately arranged, (PL 27, fig. 6), 



