250 ALQyE DIATOMACEiE. [Diatoma. 



90. Fragilaria. Lyngb. Fragilaria. 



Frustula forming plane, pseudo-articulated, densely striated, fra- 

 gile filaments, separating at the strias (not cohering at their 

 angles.) — Name, from their fragile character. Grev. 



1. F. pectinalis, Lyngb. Pectinated Fragilaria. Filaments 

 rigid, attenuated, densely striated, the joints 3 — 4 times broader 

 than they are long. Grev. — Grev. in Hook. Br. Fl. v. ii. p. 403. 

 — Conf. pectinalis, Dillw. t. 24. E. Bot. t. 1611. 



Rivers and stagnant waters. Near Limerick ; W. H. Harvey. 



91. Diatoma. Ag. Diatoma. 



Frustula forming pseudo-articulated, iplane Jilaments, at length 

 separating and cohering at their angles. — Name ; Siarofirj, 

 incision ; from the divisions as far as the angles, which co- 

 here. Grev. 



* Frustula (or joints) rounded. 



1. D. auritum, Lyngb. Auricidated Diatoma. Filaments 

 yellow, the joints quadrate, rounded, with an auricle at each 

 angle. Grev — Grev. in Hook. Br. Fl. v. ii. p. 404. Lyngb. 

 Hyd. Ban. p. 182. t. 62. 



Very rare. At Youghal parasitic on Cal. polyspermum ; Miss 

 Ball. 



2. D. obliquatum, Lyngb. Oblique-jointed Biatoma. Fila- 

 ments short, unequal, the joints half as long again as they are 

 broad, punctate, and transversely banded. Grev. — Grev. in 

 Hook. Br. Fl. v. ii. p. 405.— Conf. obliquata, E. Bot. t. 1869. 



Parasitic on marine Algae : very rare. Ardinairy Point, Wicklow, 

 on Griffithsia simplicifilum ; W. H. Harvey. 



•* sfs Frustula (or joints) square, (not rounded.) 



3. D. striatulum, Ag. Banded Biatoma. Filaments some- 

 what curved, pellucid at the articulations, the joints nearly as 

 long as they are broad, densely and transversely striated. 

 Grev. — Grev. in Hook. Br. Fl. v. ii. p. 405. — Conf. striatula, 

 E. Bot. t. 1928. 



Parasitic on marine Algae, particularly Cladostephus spongiosus 

 and verticillatus ; not uncommon. A very handsome species, with 

 curved glossy filaments half an inch or more in length. 



4. D. marinum, Lyngb. Tcenia-like Diatoma. Filaments 

 unequal, the joints longer than they are broad, with a trans- 



