288 Proceedings of the Royal Irish Academy. 
Odontidium tenue, (Kiitz.) Fresh water. 
Frustules united in short filaments ; on side view narrow, ellipti- 
eal, with sharp ends; costes numerous, with interrupted linear stric 
interposed. 
Denticula tenuis, Kitz. Bac., p. 43, T. xvii., fig. 8. Wm. Sm., 
Bp? Volou.;%p. 20, Pi. xxxty:, tie: 290." Ralfeein Prive, te fo 
Rab? FI. Hur:;' sect: 1, p. 114: 
Powerscourt, Co. Wicklow. River Dour, Co. Cork. 
Odontidium inflatum, (Wm. Sm.) Fresh water. 
Frustules united in short filaments; on side view short, broadly 
elliptical, costze close. 
Denticula inflata, Wm. Sm., B:D., Vol. u.5..p..20, Pl: xxxiv., 
fig. 294. According to Ralfs, = Denticula crassula, Nageli. Rallis, 
in Pritek., pid (d2,.Rab, El. Erur., sect. bo qodd a: 
River Dour, Co. Cork. 
Odontidium elegans, (Kutz.) Fresh water. 
Frustules united in short filaments, on front view slightly ellipti- 
eal; truncate, with large glandular expansions at the ends of the 
costz; on side view, narrow, elliptical, pointed at the ends; coste 
close. 
Denticula elegans, Kiitz., p. 44, T. xvii., fig. 5. Rab. Siissw. 
Diats ps 383, Toa, figs4. ~ Ralis,ansPriteh., p: i7o,vk |. aaa eine 4 
Grunow, Verhand der K. K. Zool. Bot. Gesel., Band xii., 1862, p. 549. 
Rab. Fl. Eur., sect. 1, p. 115.—Denticula ocellata, Wm. Sm., B. D., 
Moly 11.,,pz 20. 
Rocks, Bundoran, Co. Donegal. Powerscourt, Rathdrum, Co. 
Wicklow. Rocks near the sea at Black Castle, and the Silver sands 
in the neighbourhood of Wicklow. Rocks, Portrush, Co. Antrim. 
This species has usually been found by me on moist rocks. 
Genus IVY. Dnrrerecrammua, Ralis. 
Frustules in short filaments, parallel to each other. On the front 
view slightly constricted near the ends; on side view elliptical, stri- 
ate; the stric marginal. 
This genus, in the general appearance of its frustules, 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 shght constriction at the ends. 
