Bacillaria.] THE infusoria. 219 



286. Bacillaria seriata. The spotted Bacillaria has a 

 slender straight lorica, eight or nine times longer than it 

 is broad ; the ova grains are divided into four or five 

 masses. Found amongst conferva. Length 1 -360th. 



287- Bacillaria Ptolemaei. Ptolemy's Bacillaria is 

 very small and smooth (?) length, twice or thrice its 

 breadth. Colour pale. Found in Alexandria. Length 

 l-3600th. 



Genus LXII. Tessella. The flat-chain Animalcules are 

 free, for though often entangled together, they are never 

 attached ; they are covered with a simple bivalved or mul- 

 tivalved siliceous lorica, prismatic in shape, and (dilated 

 and compressed) into the form of a table. In consequence 

 of perfect self-division of the lorica, and imperfect division 

 of the body, they are developed in the form of gaping 

 chains or zig-zag polypi clusters. The articulations are 

 mobile, and in the form of a plate (not wand or rod-shaped). 

 In organization they stand between Achnanthes and 

 Bacillaria. No opening in the lorica has been distinctly 

 seen ; longitudinal clefts are present, and essentially 

 characterize this genus. The ova cluster has numerous 

 lappets, and looks like a great number of roundish 

 yellowish-green coloured spots, which are not the ova 

 themselves, but the structure containing them. 



288. Tessella catena. The striated Tessella has a 

 plate-like lorica, often broader than it is long ; it has from 

 four to twenty-four longitudinal series of transverse striae. 

 (See fiff. 180, 181, and 182.) Found amongst Ceramia 

 and other sea-weeds. Length of table (that is, breadth of 

 the bands) l-570th to 1 -240th. 



289. Tessella arcuata. The smooth Tessella is nearlv 



