288 Proceedings of the Royal Irish Academy. 



Odontidium tenue, (Kiitz.) Fresh, ^vater. 



Prustules miited in short filaments ; on side vie-w narrow, ellipti- 

 cal, with sharp ends ; cost^ numerous, "with interrupted linear strife 

 interposed. 



Denticula tenuis, Kutz. Bac, p. 43, T. xvii., fig. 8. "Wm. Sm., 

 B.D., Yol. ii., p. 20, PL xxxir., fig. 293. Ealfs, in Pritch., p. 773. 

 Eah. PL Eui'., sect. 1, p. 114. 



Powerscourt, Co. AVicklow. Eiyer Dour, Co. Cork. 



Odontidium inflatum, ("Wm. Sm.) Presh. water. 



Prustules united in short filaments ; on side riew short, broadly 

 elliptical, costse close. 



Denticula inflata, "Wm. Sm., B. D., Yol. ii., p. 20, PI. xxxiv.,. 

 fig. 294. According to Palfs, = Denticula crassula, ISTageli. Palfs, 

 in Pritch., p. 773. Eab. PL Eur., sect. 1, p. 115. 



Eiver Doiu', Co. Cork. 



Odontidium elegans, (Kutz.) Presh water. 



Prustules united in short filaments, on fi'ont view sligLtly ellipti- 

 cal; truncate, with large glandular expansions at the ends of the 

 costse ; on side view, narrow, elliptical, pointed at the ends ; costse 

 close. 



Denticula elegans, Kiitz., p. 44, T. xvii., fig. 5. Eah. Siissw. 

 Diat., p. 33, T. 1., fig. 4. Ealfs, in Pritch., p. 773, PL xiii., fig. 4. 

 Grunow, Yerhand der K. K. Zool. Bot. GeseL, Band xii., 1862, p. 549. 

 Eab. PL Eur., sect. 1, p. 115. — Denticula ocellata, "Wm. Sm., B.D., 

 Yol. ii., p. 20. 



Eocks, Bundoran, Co. Donegal. Powerscourt, Eathdnim, Co. 

 "Wicklow. Eocks near the sea at Black Castle, and the Silrer sands 

 in the neighbourhood of "Wicklow. Eocks, Portrush, Co. Antrim. 

 This species has usually been found by me on moist rocks. 



Genus lY. DnEEEE&EJOi^iA, Ealfs. 



Prustules in short filaments, parallel to each other. On the front 

 view slightly constricted near the ends ; on side view elliptical, stri- 

 ate ; the striae marginal. 



This genus, in the general appearance of its fi-ustules, bears a strong 

 resemblance to some of the forms included in Odontidium and Denti- 

 cula, to which latter Gregory assigned the numerous forms described 

 by him, but may be distinguished by the fact that the margin on front 

 view presents a slight constriction at the ends. 



