NAVICULA. 187 



8 to 10 in 1 c.d.m. in the large forms, 12 to 14 in the small. Length, 2-5 to 

 4-5 c.d.m. Median breadth, 1.25 to 175 c.d.m. 



Fresh water. Antwerp and probably elsewhere England (Kitton), Ireland (Donk. O'Meara), 

 Scotland (Greg). 



var. Placentula. (A; Placentula Ehr., H.V.H. Atl., pi. 8, f. 26 and 

 28*), plate 3, fig. 135. 



Apices somewhat more inflated, striae 6 to 9 in 1 c.d.m., those 

 surrounding the central nodule not alternately long and short. 



Brackish water Antwerp (rather common). 



N. Anglica Ralfs. (in Pritch. Inf., p. 900, N. tumida W. Sm. ; 

 H.V.H. Atl., pi. 8, f. 29*, in Type No. 59), plate 3, fig. 136. 



Does not differ essentially from the preceding species, to which it is 

 closely connected, except that its apices are rostrate-capitate. Striae 10 to 12 

 in 1 c.d.m. 



Fresh water England, Ireland. 



var. subsalina Grun. (H.V.H. Atl, pi. S, f. 31*), plate 3, fig. 137. 

 Apices rostrate, scarcely somewhat capitate. 



N. crucifera Grun. See this form after N. cancellata, with which it 

 is closely allied. 



N. Semen Ehr. (Verb. Amer., 1843, pi. IV. ii., f. 8; W. Sm., 

 S.B.D., i., p. 50, pi. 16, f. 141*; H.V.H. Type No. 98) ; plate 25, fig. 718. 



Very variable in outline and size, in general very similar to N. gastruui, 

 from which it differs in possessing an oval-oblong valve with apices somewhat 

 constricted, very obtuse. Striae reaching throughout to the raphe and central 

 nodule ; robust, finely divided transversely, all radiate, the terminal ones very 

 approximate 9 to 10 in 1 c.d.m., the median, very distant, about 5 in 1 

 c.d.m. Length, 5 to 7 c.d.m. Breadth, at the median portion, 2 to 2-5 c.d.m. 



Fresh water Belgium ? probable. England, France, Holland. Found in many fossil deposits. 



N. Capitata Ehr. (Inf., p. 185, n. 240, pi. 13, f. 20*; Schumann, 

 1862-69, f. 34*); plate 25, fig. 719 a.b. 



Valve small, oblong, inflected in the median portion, abruptly inflated at 

 the apices, which are rostrate not capitate. Striae distinctly punctate, radiate, 

 5 to 7 in 1 c.d.m., not reaching to the raphe, and leaving a rather large 

 hyaline area round the central nodule. Length, 2 to 4 c.d.m. 



Fresh and brackish water. Throughout Europe. 



