250 ALGM DIATOMACEyE. [Diatoma. 



90. FRAGILARIA. Lyngl. Fragilaria. 



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

 gile filaments, separating at the striae (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, plane filaments, at length 

 separating and cohering at their angles. Name ; SicnofjLrj, 

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

 here. Grev. 



* Frustula for joints ) rounded. 



1. D. auritum, Lyngb. Auriculated 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. Dan. p. 182. t. 62. 



Very rare. At Youghal parasitic on Col. potyspermum ; Miss 

 Ball. 



2. D. obliquatum, Lyngb. Oblique-jointed Diatoma. 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 Grijfithsia simplicifilum ; W. H. Harvey. 



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



3. D. striatulum, Ag. Banded Diatoma. 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. Tcerda-like Diatoma. Filaments 

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



