318 Proceedings of the Royal Irish Academy. 



ends of the diapkragms alternate ; valres much exj)aiided in middle ; 

 strongly costate : costae perrious. 



Tetracydus laciisfris, (Ealfs.) Fresh, water. 

 IMiddle expansion of the valve rounded. (Plate 29, fig. 4.) 

 EaKs, Ann. Xat. Hist., Yol. sii., 1843, PL ii., fig. 2. Kiitz. Bac., 

 p. 127, T. xxix., fig. 70. Eah. Siissw. Diat., p. 68, T. ix., fig. 1. 

 Wm. Sm., B. D., Yol. ii., p. 38, PL xxxis., fig. 308. Ealfs, in Priteh, 

 p. 806, PL viii., fig. 10, and PL xi., fig. 24, 25. Grunow, Yerhand 

 der X. K. Zool. Bot. GeseL, Band xii., 1862, p. 412. Clevc, Om 

 Svenska och Xorska Diat., p. 222. 



Eiver Erne, Crossdoney, Co. Cavan. Lake near Castlewellan, Co. 

 Down. Eiver Bann, Yerner's Bridge, Co. Armagh. Tonabrick IMoun- 

 tain, Co. Cork ; Y'm. Smith. 



Tetracydus emaryinatus, (Ehr.) Fresh water. 



"Yalves constricted towards the extremities, which are rounded 

 and suh-apiculate ; infiections deeply notched or cmarginate • otherwise 

 like the last species." — AYm. Smith. 



lYm. Sm. B. D., Yol. ii., p. 38. Ealfs, in Priteh., p. 806. Grunow, 

 Yerhand. der K. K. Zool. Bot. GeseL, Band xii., 1862, p. 412. Eab. 

 Fl. Etir., sect. 1, p. 302. Cleve, Om Svenska och XorskaDiat., p. 222. 

 Smith supposes this specie's identical with Biblarium emarginatum, 

 Ehr. ITic. T. xxxiii. 2, fig. 6. On his authority I attribute the 

 species to Ehrenberg. 



Gap of Dunloe, Killarney. YTm. Smith. This species is extremely 

 rare, not a single specimen having ever come under my notice from 

 any locality in Ireland. 



Genus lY. EHAjjnoxEirA, KUtz. 



Stipes short ; diaphragms numerous, on the external margin 

 strongly costate, broad ; extremity of the valves unstriate. 



Smith alleges that in this genus the valves have a median line, a 

 statement which does not appear to be sustained by the facts of the 

 case. 



Rhabdonema arcuatuyn, (Lyngb.) Marine. 



Frustules short ; on side view broadly elliptical ; costate, with 

 monilif orm striae interposed between the costse ; striae pervious ; dia- 

 pliragms numerous, parallel, with a single foramen. (PL 29, fig. 5.) 



Kiitz. Bac, p. 126, T. xviii., fig. 6, who states that the species is 



