DICKTEIA. 233 



Valves lanceolate, with apices very slightly produced, subobtuse ; striae 

 about 14 in 1 c.d.m., reaching almost to the raphe, gently radiate, finely 

 divided transversely, with divisions simulating longitudinal striae. Length, 

 about 5 c.d.m. 



Marine. Blankenberghe. England, France, Bahusie. 



var. setaceum Kutz. (S. setaceum Kiitz.), H.V.H. Atl., pi. 15, f. 13*), 

 plate 5, fig. 245. 



Differs from the preceding by shorter valves, and strice more strongly 

 radiate. Length, about 25 c.d.m. 



Marine. Blankenberghe. France, Bahusie. 



Sub-genus III. Dickieia. 



Navicula enclosed in fohciceous fronds. Marine habitat. 



N. ulvacea (Berk.) H.V.H. {Dickieia ulvacea Berkeley in 

 Kiitz. Baa, p. 119; Sp. Alg., p. 109; H.V.H. Atl., pi. 16, f. 10*), plate 27, 

 fig. 7 8x - 



Valves elliptic, with apices obtuse rounded. Raphe surrounded by a very 

 narrow hyaline area, dilated into a false stauros at the median portion ; striae 

 16 in 1 c.d.m., radiate, robust, finely divided transversely. Length, 8*5 to 

 i2 - 5 c.d.m. Breadth, 2-5 to 3^5 c.d.m. Frustules scattered in gelatinous 

 leaf-like fronds. 



Marine. Aberdeen, Scotland (Dickie!), Ireland (O'M.). 



N.B. -The Dickieia pinnata Ralfs and D. Dansci Thw. are not entered 

 here, the first is a Schizonema and the second a Mastogloia. 



The genus Navicula is very vast, and includes at least 1,000 forms. It is 

 therefore conceived that authors, especially those who have had to describe 

 the forms of the whole world, have endeavoured to simplify these difficulties 

 by arranging forms into a certain number of groups which they have elevated 

 into the rank of genera. Some of these genera have been admitted into the 

 present work, but it is still necessary to make a few remarks about others, and 

 to indicate their characters. They will be found here in alphabetical order. 



Alloioneis Schumann. (1867). Navicula? rhomboidal in transverse 

 section. Valves showing long striae on one side of the raphe and shortened 

 striae on the other. About half a dozen exotic forms belong to this section. 



Anomaeoneis Pfitzer. (187 1, Ueber Bau., etc.). This group- 

 corresponds with my group of Sculptcce, 



