308 Proceedings of the Royal Irish Academy. 



adds, that " lie considers Grunow has rightly regarded it as a variety 

 of Synedra splendens." — Synedra splendens, var. longissima, Grnmow, 

 Verhand. der. K. K. Zool. Bot. Gesel., Band xii., 1 862, p. 397. Grunow 

 considers this form identical with Synedra biceps, Kiitz. Bac, p. 66^ 

 T. xiv., figs. 18 and 21, and Bab. Siissw. Diat., p. 55, T. v., fig. 9.. 

 But however this may be, Synedra longissima and Synedra biceps are 

 in reality distinct species. 



Pond in Botanic Gardens, Belfast. Malahide. St Penton's "Well, 

 Sutton. Streamlet, IN'ewcastle Lyons, Co. Dublin. Twyford Lake,, 

 near Athlone, Lake Belvidere, Co. Westmeath. Ditch near railway- 

 station, Dundalk, Co. Louth. Ditch near Wicklow. 



Synedra ohtusa, (Wm. Sm.) Presh water. 



Similar to the preceding species, but much shorter ; not so much 

 constricted or expanded at the rounded ends. (PL 28, fig. 28.) 



"Wm. Sm., B. D., Vol. i., p. 71, PL xi., fig. 92, who regards it as 

 = Synedra ulna, Ehr. Inf., T. xvii., fig. 1 ; but of this he is doubtful ;^. 

 and Synedi-a aequaKs, Kiitz. Sp. Alg., p. 45, ad speciem quae dedit 

 amico DeBrebisson. If Synedi'a sequalis, Kiitz., just referred to, be 

 the same as that described by the same author, Bac, p. 66, T. xiv., 

 fig. 14, it is scarcely 'identical with the present species. — Synedi'a 

 splendens, var. obtusa, Grunow, Verhand. der K. K. Zool. Bot. 

 GeseL, Band xii., 1862, p. 397. — Synedra splendens, var. ^qualis, 

 Eab. PL Eur., sect. 1, p. 134. The linear form of the side view 

 appears to me to distinguish this from the form named Synedi'a splen- 

 dens by both the authors last referred to, which Grunow describes as 

 generally, small lanceolate, and less frequently linear, and Rabenhorst 

 as linear, lanceolate. If this form can be regarded as a variety of any 

 other, I think it should be of Synedi-a longissima, which it very closely 

 resembles. 



Tacumshane, Co. "Wexford ; Ditch near railway station, London- 

 derry. Limestone quarry, MuUingar. Twyford Lake, near Athlone.. 

 Lake Belvidere, Co. "W'^estmeath. 



(e). Stri(B interruptedly a narrow, longitudinal sulcus ; valves, narrow 

 elliptical. 



Synedra sploidens, (Kiitz.) Presh water. 



Prustules long : on front view usually wider at the ends than in 

 the middle ; on side view, narrow elliptical, gradually attenuated to- 

 the slightly capitate ends. (PL 28, fig. 29). 



I have found it impossible to discriminate between this species- 

 and Synedra ulna, as described by "Wm. Sm., B. D., Yol. i., p. 71^ 

 PL xi., fig. 90. The latter species, as described by Kiitzing Bac.,. 

 p. 66, T. xxxx., fig. 28., is on side view perfectly linear; and. 

 although I have occasionally seen specimens which exhibit a ten- 



