2T4 NAVICULA. 



Valve very elongate, linear, gently inflated at the median portion and at the 

 apices; raphe not surrounded by a hyaline area; longitudinal and transverse 



stria? delicate, cutting one another at right angles, equally distant, about 20 in 

 1 c.d.rn. Length, 13 to 14 c.d.m. Breadth at the median portion, 1 c.d m. 



Brackish water. Not yet found in Belgium. England, Ireland, France. 



var. Belgica H.V.H. (H.V.H. Atl. Supp., f. 29*), plate 4, fig. 189. 



Much smaller than the type form and with very pronounced inflations. 

 24 striae in 1 c.d.m. Length, 6 to 7 c.d.m. Breadth at the central 

 inflation, 075 c.d.m. 



Brackish water. Ostend (Charles Petit). 



XIII. Crassinerves. 



{ Valve lanceolate, with apices not rostrate-capitate . . N. cuspidata. 



-{ Valve with apices rostrate-subcapitate *. N. ambigua. 



(. Valve rostrate-subcapitate, showing transverse thickenings . . forma craticula. 



N. CUSpidata KlltZ. (Baa, p. 94, pi. 11, f. 24 and 37; H.V.H. 

 Atl., pi. 12, f. 4*), plate 4, fig. 190. 



Valve broadly lanceolate, with apices gently inflated, not rostrate ; trans- 

 verse striae gently radiate, almost perpendicular to raphe, fine, reaching 

 almost to the raphe, 14 in 1 c.d.m. Longitudinal striae fine and more 

 compact. Length, about 9 c.d.m. Breadth, 2-3 c.d.m. 



Fresh water. Common throughout Europe. 



var. halophila Grun. (H.V.H. Atl. Supp., f. 30*; in Type No. 12), 

 plate 4, fig. 191. 



Narrow, very small: about 5 c.d.m.; striae delicate, about 16 in 1 

 c.d.m., radiate near the median portion, convergent at apices. 



Brackish water. Blankenberghe. 



N. ambigua Ehr, (Amer., 1843, p. 129, pi. II. 2, f. 9; H.V.H. 



Atl., pi. 12, f. 5*; Type No. 121), plate 4, fig. 192. 



Differs from the preceding, of which it is probably only a variety, by its 

 smaller size, and its apices which are rostrate-capitate. Length, 6 to 7 c.d.m. 

 Breadth, 1*5 c.d.m. 



Fresh water. Common throughout Europe. 



forma craticula. (H.V.H. Atl., pi. 12, f. 6*; Type No. 122), plate 

 4> fig- 193- 



Valve showing transverse thickenings. 



