230 SCHIZONEMA. 



somewhat dilated near the central nodule. Stria gently radiate, very fine, 

 distant, about 28 in 1 c.d.m. Frustules with girdle face quadrangular, united 

 into long filaments. Length, - 8 to 1*5 c.d.m. Breadth, about '3 c.d.m. 



Fresh water. Brussels (Delogne). England, France. 



** Valve with margin not furnished with coarse beads. 



N. Flotowii Grun. ! (H.v.h. Atl., pi. i 4 , f. 41*; Type No. 48), 



plate 5, fig. 238. 



Valve linear, with apices rounded, median portion inflated. Raphe 

 surrounded by a considerable hyaline zone, and much dilated at the median 

 portion. Striae radiate, fine, 35 in 1 c.d.m. Length, 1*5 c.d.m. 



Freshwater. Frahan (Del.). 



N. contenta Grun. ! (H.V.H. Atl., pi. 14, f. 31*, sub. n. N. 



ttinodis ; Type No. 146), plate 5, fig. 239. 



Valve linear, inflated at the median portion and at the apices. Raphe 

 surrounded by a considerable hyaline zone, only just a little dilated near the 

 central nodule. Striae very delicate, almost parallel, about 36 in 1 c.d.m. 

 Length 7 to t c.d.m. Breadth, 2 to '025 c.d.m. 



Humid positions. In a slate quarry at Rochehaut (Del.) 



var. biceps. (H.V.H. Atl., pi. 14, f. 31**), plate 5, fig. 240. 



Differs from the type form by the central inflation, which is very slight 

 or absent. 



Groenendael (Delogne). 



Observ. The group " Minutissimce " is not a natural group. The species 

 included in it ought to be incorporated in the other groups previously 

 mentioned. If all these forms, which have nothing in common but their 

 small size, are allowed to remain grouped, it is only to facilitate comparison 

 and consequently the determination of the different species. 



B. Naviculse not free. Frustules naviculoid, inclosed in 

 tubes or gelatinous-mucous fronds. 



Sub-genus II. Schizonema. 



Frustules naviculoid, generally feebly silia'ous, enclosed in mucous tubes which 

 simulate the higher algce. Habitat : maritte. 



I agree with Mr. Grunow that it is preferable to preserve distinct the 

 Naviculce belonging to the old genus Schizonema on account of the character 



