406 



NITZSCHIA. 



var. incurva Grun. (H.V.H. Atl., pi. 70, f. 13 and 14*), plate 17, 

 fig- 573- 



Small, often taking up such a position (fig. 573 left-hand figure) that it 

 appears quite straight, 6 or 7 carinal dots in 1 c.d.m. Central striae, 14*5 ; 

 terminal, 18 to 20 in 1 c.d.m. Length, 5 to 6 c.d.m. Breadth of 

 valves, about "5 c.d.m. 



Marine. Between Oscillatoria on posts in the harbour of Ostend (Grunow). 



Obs. Synedra hamata IV. S//i. ! is not a Nitzschiella as seated by Raben- 

 horst and De Toni (Syllog., p. 550) ; it is a true Synedra, or rather a mon- 

 strosity of Synedra, with hamular apices. The striae are marginal, about 10 in 

 1 c.d.m., and the hyaline area is lanceolate. I think therefore this form may 

 be regarded as belonging to S. afftnis. 



The genus Homoeocladia Ag. (1827) is analogous 

 to the genus Schizonema, that is to say, it is established for 

 certain Niizschia, which live in mucous tubes. I cannot 

 admit this genus any more than Schizonema. 



Three forms on our shores are included in the group or 

 . sub-genus Homoeocladia. 



Fig. 127. D 



H. subcohcerens Grun. 

 var. Scotica, 



N. (H.) Martiana Ag. (Consp., p. 25 ; w. Sm., S.B.D., ii., p. 80, pi. 



55. f- 347*), Plate 33, fig. 881. 



Valves linear, lanceolate, with obtuse apices. Keel central, with 5 or 6 



dots in 1 c.d.m. Transverse striae very fine, with difficulty visible, more than 



30 in 1 c.d.m. Girdle face linear, lanceolate, with obtuse apices. Length, 



16 to 28 c.d.m. Frustules generally collected together in dense fascicles 



nclosed in rugose fronds, simple or divided dichotomously. 



Marine. On all the maritime coasts of Europe. 



N. (H.)filiformis, W. Sm. ! (S.B.D.,ii., p. 80, pi. 55, f. 348*), plate 

 33, fig- 882. 



Valves linear, lanceolate, with subacute apices. Keel central, with 5 or 6 

 dots in 1 c.d.m. Striae fine. Girdle face linear, lanceolate, obtuse. Length, 

 about 10 c.d.m. Frustules collected in groups of 3 or 4 in filiform, simple, 

 undivided fronds. 



Fresh and brackish water. Bexhill, Lewes, England (W. Sm, !), Liverpool (Comber), near 

 Hull (Norman), Ireland (O'Meara). 



