NAVICULA. 165 



Var. Dactylus. (N. Dactylus E/ir., H.V.H. Atl., pi. 5, f. 1*; Type 

 No. 51), plate 2, fig. 68. 



More robust than the preceding, with inflations absent or only 

 slightly marked ; costse generally not so long and more robust, about 

 4*5 to 1 c.d.m. 



Fresh water. Heyst (J. Deby). 



Var. gentilis (N. gentilis Donk.,m H.V.H.'s Typ. Syn., Nos. 53 

 and 481). 



Absolutely similar to N. nobilis, but much smaller in all parts ; 

 it may be considered as a dwarf form of N. nobilis. Length. 14 

 to 20 c.d.m. ; costal about 7 in 1 c.d.m. 



Fresh water and fossil deposits. England, Scotland, Lough Mourne (Ireland), etc. 



N. major Kutz. (Baa, pi. 4, f. 19 ; H.V.H. Atl, pi. 5, f. 3-4* ; 

 Type No. 54), plate 2, fig. 69. 



Valve linear-elliptic, more or less inflated in the median portion, 

 apices not inflated, somewhat conical. Costre robust, 5 to 7 in 1 c.d.m., 

 feebly radiate, rather approximate to raphe, and leaving an oblong hyaline 

 space round the central nodule. Length, 18 to 30 c.d.m. 



Fresh water. Everywhere. 



The Navicula major passes imperceptibly into the following : 



N. viridis Kutz. (Baa, pi. 4 , f. 18; h.v.h. Atl, pi. 5, f. 5*; 

 Type No. 56), plate 2, fig. 70. 



Valve linear-elliptic, without inflations, apices rounded. Costae about 

 7 in 1 c.d.m., rather approximate to the raphe, and leaving scarcely 

 any marked space round the central nodule ; radiate at the middle of 

 the valve, convergent towards the apices. Length, very variable, from 

 5 to 20 c.d.m. 

 Fresh water. Everywhere. 



Var. commutata Grun. {Nav. Jiemipieni and. ncc Kutz. 

 H.V.H. Atl., pi. 5, f. 6*; Type No. 57), plate 2, fig. 71. 



Valve elliptic-linear, considerably attenuated at the apices ; costs 

 slender, attenuated round the central nodule, about n in 1 c.d.m. 



The two valves are dissimilar : one has striae covering the whole 

 valve ; in the other the striae are interrupted (see the figure) 

 unilaterally, near the central nodule. Length, about 4 to 6 c.d.m. 



Fresh water. Manage (P. Gautier). 



N. cardinalis Ehr. (Americ.L, r, w> n W , 21, Ii.V.H. Atl. Supp., 

 f. 5* ; Type No. 60), plate 2, fig. 72. 



