BaciUaria.] THE INFUSORIA. 207 



230. Navicui^a trochus. The fly-wheel Navicula is 

 smooth ; the lorica is enlarged at the centre and con- 

 stricted at the ends. The central opening is round, and 

 the lorica has several longitudinal striae. Found fossil, 

 in Sweden. Length 1 -860th. 



231. Navicula follis. The tube-like Navicula is 

 smooth, and has a short depressed lorica, swelled at the 

 middle, but no longitudinal striae. Found fossil, at Santa 

 Flora, in Tuscany. Size l-2300th. 



232. Navicula? trinodis. The three-bellied Navicula 

 is smooth, has a linear elongated lorica, having a slight 

 turgidity at the middle of one side. Found fossil, at 

 Degernfors, in Sweden, &c. Size l-860th to 1 -480th. 



233. Navicula cari. The carvs Navicula is smooth, 

 and has a slender lanceolate lorica, acute at all sides. 

 Found fossil, at Cassel. Size l-1150th. 



234. Navicula ? quadricostata. The four-ribbed Navi- 

 cula has a slender ovato-oblong lorica, with four longitu- 

 dinal striae or ribs, and is truncated at both ends. Found 

 in mineral water, at Carlsbad. Size 1-1 720th to l-860th. 



235. Navicula Baltica. The Baltic Navicula is smooth, 

 and has a sigmoid- shaped lorica, straight and linear at the 

 middle, and obtuse at the ends, as shewn at fig. 144. 

 The interior is of a yellow golden colour, and the central 

 opening appears small and round; no motion has been 

 seen. Found in phosphorescent sea- water. Length 1- 70th. 



236. Navicula hippocampus. The little sea-horse 

 Navicida is smooth ; lorica sigmoid, lanceolate. (See 

 group 145.) Sometimes it has delicate longitudinal striae. 

 Found in fresh and salt water. Size l-90th to l-70th. 



237. Navicula sigma is smooth, has a lanceolate sig- 



