ACHNANTHES. 28 1 



Lower valve without stauros. 



a UPPER VALVE ONLY DIFFERING FROM THE LOWER VALVE BY THE 

 ABSENCE OF NODULE AND RAPHE. 



b. Valves broadly lanceolate or elliptic-lanceolate. 



A. delicatula Kutz. (Bac., p. 75, pi. 3. f. 21 ; H.V.H. Atl., pi. 

 27, f. 3 and 4* ; Type No. 234), plate 8, fig. 330. 



Valves broadly lanceolate, with apices very frequently produced, rostrate, 

 subacute, having about 15 robust striae, feebly radiant in 1 c.d.m. ; lower 

 valve with median striae shortened ; raphe surrounded by a narrow median 

 zone, somewhat dilated into a rounded area round the central nodule. Length 

 1 to 2 c.d.m. 



Brackish water. Antwerp (H.V.H. , Type No. n). England (H.V.H. , Type No. 234). 



A. Biasolettiana Grun. (Arct. D., p. 22; H.V.H. Atl., pi. 27, 



f. 27 and 28*; Type No. 237), plate 8, fig. 331. 



Valve lanceolate, with apices rounded, obtuse, median portion inflated, 

 striae fine, feebly radiant, 22 to 28 in 1 c.d.m. ; lower valve with central nodule 

 surrounded by a small rounded hyaline area. Length, about 1 c.d.m. 



Fresh water. Brussels (Delogne). 



bb. Valves narrowly lanceolate or linear. 



A. microcephala Kutz. (Bac, p. 75.pl. 3, f. 13 and 19; H.V.H. 



Atl., pi. 27, f. 20-23*), plate 8, fig. 332. 



Valves very narrowly lanceolate, apices capitate, having 30 to 36 feebly 

 radiant striae in 1 c.d.m. ; upper valve with all striae of equal length, except 

 the median, which is somewhat shorter; lower valve with a much shortened 

 median striae, leaving an elongated hyaline area near the central nodule 

 Length, 1 to 1*5 c.d.m. Breadth, about "3 of a c.d.m. 



Fresh water. Groenendael (Delogne), Ard. Lieg. (De Wild). England (Comber, Norman) 

 Scotland (Baxter Coll., Nos. 2528, 2904), Ireland (O'Meara). Found almost everywhere. 



A. exilis Kutz. (Alg. aq. dulc, 1833, No. 12; Bac, p. 76, pi. 21, 

 f. 4 ; H.V.H. Atl., pi. 27, f. 16-19*; m Type No. m), plate 8, fig. 333. 



Valves narrowly lanceolate, apices rounded, subobtuse, striae somewhat 

 radiate, 26 to 27 in 1 c.d.m. ; the median more robust, more distant (19 to 21 



