Navlculacea.l infusorial animalcules. 409 



Navicula gracilis. — Smooth, slender, lanceolate; ends acute 

 laterally, linear, truncate. Common ; freshwater and fossil. Length 

 l-1500th to l-o60th. 



N. (?) pellucida = AmiMplmra pcUiicida (Kiitz.) — Slender, lan- 

 ceolate, smooth (no median aperture, Kiitz.), see fig. 140, which 

 rei^resents a group, and a transverse section, to show the position of 

 the central furrow on each side. Found -ndth the preceding. Length 

 1 -300th to 1 -140th. It has the general form of a Closterium ; and 

 the apparent absence of an umbilicus, would certainly determine its 

 position with some other genus than Navicula. 



N. mm (1838) r= Ceratoneis acus (Ehr.) and Synedra sultilis (Kiitz.) 



N. umhonata. — Smooth, sti'aight, constricted near the middle, 

 causing the ends to appear larger, hence its name. Length 1 -430th 

 to 1 -240th. Salt and fresh water, and fossil. Kiitzing adduces 

 this as his Surirella thermalis, and the Pinnularia (?) thermalis of 

 Elirenberg ; and, as is thus implied, furnished with transverse striae, 

 delicate though they are. If such striae exist in any degree, this 

 species should certainly be excluded from the present sub-genus. 



K. fulva. — Smooth, broadly lanceolate ; slightly produced at the 

 ends in the form of a beak or rostrum (^. e. ends rostrate), colour 

 yellowish-brown; umbilicus -very small, round; lateral aspect 

 narrowly linear and truncate. Length 1-1 150th to 1-1 80th (P. 15, 

 f. 5.) Alive and fossil. 



IT. amphish^na. — Smooth, broadly elliptic (see group 141), apices 

 much contracted ; umbilicus circular ; granular contents of golden- 

 yellow colour. Ehrenberg remarks, that the vibratile process, seen 

 by Bory St. Yincent, was, in fact, the locomotive organ, the action of 

 which is readily seen, though the process protrudes but a very little 

 beyond the lorica. Length 1-1 700th to 1 -240th. Ercsh water. 



N. nodosa. — Smooth, linear, -ndth three undulations on each side, 

 about the middle ; extremities contracted, shortly rostrate and obtuse 

 (see fig. 143.) Central opening round. Length 1 -430th. 



X. Cari. — Slender, lanceolate, smooth ; ends acute ; umbilicus 

 circular. Length 1-1 150th. Fossil at Cassel. 



N. Baltica. — Large, smooth ; sigmoid, by the curvatui'e of the 

 attenuated obtuse ends in opposite directions (fig, 144.) Central 



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