350 DIATOMA. 



Very narrow, delicate, with apices feebly capitate ; length, 3 to 5 

 c.d.m. 



The type-form and the variety, which are allied by various intermediary forms, appear in 

 the brackish water gathering (Type Xo. 337) made at Nieuport (West. No. 799). Ireland 

 (O'Meara). 



var. hybrida Grun. (H.V.H. Atl., pi. 50, f. 10-13*), plate 11, 

 fig. 469. 



Valves more robust, more broadly linear, strongly capitate, with head 

 extending considerably beyond the breadth of the valve. Length, 5 to 

 8 c.d.m. 



Brackish water. Common : Antwerp. 



var. Ehrenbergii. (D. Ehrenbergii Kutz.). Only differs from the 

 last mentioned variety by its valves being attenuated underneath the 

 capitate apex. 



II. ODONTIDIUM AUCT. Frustules united in short filaments ; 



costce very robust. 



D. hiemale (Lyngb.) Heib. (Odontidium Kutz., Bac., p. 44, 

 pi. 28, f. 4; H.V.H. Atl., pi. 51, f. 1 and 2* ; Type No. 340), plate 11, fig. 

 470. 



Valve lanceolate, with apices sometimes somewhat produced, furnished 

 with 6 to 10 robust transverse costce; striae fine, about 20 to 22 in 1 c.d.m. 

 Girdle face quadrangular, elongated. Length, 3 to 5 c.d.m. 



Freshwater. Mountainous regions: Wiry (Del.), Ard. Lieg. (De Wild.). England, Wales 

 (Ralfs), Scotland (Greville, Arnott), Ireland (O'Meara). 



var. mesodon. (O. mesodon Kutz. ; H.V.H. Atl., pi. 51, f. 3 and 4* ; 

 in Types Nos. 347 and 461), plate 11, fig. 471. 



Valves short, very broadly lanceolate, with only 2 to 4 transverse 

 costre, placed in the middle of the valve. Length, 1-5 to 2-5 c.d.m. 



Mixed with the type-form at Wiry (Del.). England, Scotland (Arnott, Gregory), Ireland 

 (W. Sm., O'Meara). 



D. anceps (Ehr.) Grun. (Fragilaria Ehr. ; H.V.H. Atl., pi. 

 51, f. 5-8*; Type No. 341), plate [i, fig. 472. 



Valve linear, narrow, with apices rostrate or rostrate capitate, with 6 to 14 

 robust costse, having often an oblique direction; striae about 21 in 1 c.d.m. 

 Girdle face quadrangular, elongated. Length, 2 to 5 c.d.m. 



Fresh water. Mountainous regions ; Mogimont (Del), England, Norway. 



var. anomalum (O. anomahan IV. Sm.; H.V.H. Atl., pi. 51, f. 9*; 

 Type No. 342), plate 11, fig. 473. 



Differs from the type-form by internal septa shown on girdle view. 



Fresh water. Mogimont (Del.). Scotland (Balfour), Ireland (O'Meara). 



