212 DESCRIPTION OF [Polijgastrica. 



which are stretched out, by the clusters of ova within 

 them. Found at Havre, alive, and fossil in Bohemia. 

 Length l-3450th to l-60th. 



256. NAVICULA (?) undulata. The wave Navicula is 

 striated, its lorica is elliptical on the lateral surface, linear 

 and truncated on the belly, each surface having four 

 flexures, as shewn in the oblique view, fig. 149. Found 

 amongst oscillatoria. Length 1-2 10th. 



257. NAVICULA constricta. The constricted Navicula 

 is striated, has an oblong lorica, slightly constricted at the 

 middle of the ventral surface. The extremities are ob- 

 tusely truncated. Three to four striae in 1- 100th of a line. 

 Found with N. splendida. Length 1-2 10th. 



258. NAVICULA (?) amphora. The tun-like Navicula is 

 striated, has an ovate unequal lorica, swelled at one side, 

 and plane on the other. (See^. 153.) There are nine 

 delicate transverse striae in 1- 100th of a line. This 

 species is easily confounded with Cocconema cistula, when 

 the latter is without a stalk ; but the Nav. amphora is so 

 delicately striated that Ehrenberg considered it for some 

 time smooth, whilst Coc. cistula is very distinctly striated. 

 Length l-160th to l-120th. 



259. NAVICULA lineolata. The lined Navicula resem- 

 bles the preceding, but its delicate striae are longitudinal. 

 It is compressed on the ventral surface, and convex on the 

 back. Size l-280th to l-140th. 



Genus LIX. EUNOTIA. The beautiful little ship Ani- 

 malcules are free (unattached by a pedicle), inclosed in a 

 siliceous lorica, of the form of a prism, composed of one, 

 two, or more pieces or valves. The lower or ventral side 

 is flat, the other or dorsal side is convex, and often den- 



