Bacillaria.] the infusoria. 185 



167. Staurastrum dilatatum. The h'oad Staurastrum 

 has a membranovis square uniformly-granulated lorica, with 

 an opening in the centre, as shewn in fig. 101, which is 

 an empty lorica, magnified 300 times ; they are either 

 single or attached in pairs, the latter is shown at fig. 100. 

 Size l-570th. Found amongst conferva. 



168. Staurastrum joarac^o.x'wm. The slender Stauras- 

 trum is shewn at fig, 102 and 103, one of which is a 

 yellow, and the other a green, variety. They are either 

 solitary or connected in pairs. Young observers are liable 

 to mistake other forms of Bacillaria for this species ; but 

 its rough granulated surface is a special character. Size 

 1 -1200th to 1-5 70th. 



Genus XLVI. Pentasterias. The five-rayed Ani- 

 malcules. — This genus contains only one species; it is 

 distinguished by its possessing a simple univalved five- 

 sided lorica, with a central aperture, and in being free; 

 sometimes it is developed in chains. 



169. Pentasterias margaritacea. The peart Pentas- 

 terias has a granulated surface, and thick obtuse rays, 

 as shewn at fig. 104. Size 1 -540th. Found amongst 

 conferva. 



Genus XLVII. Tessararthba. The round-chain 

 Animalcules comprehend only one species (T. filiformis 

 being now considered an Odontella) ; it is distinguished 

 by a simple univalved smooth and globular lorica. While 

 imdergoing self-division it becomes chain-like, consisting 

 of four or more members. The species is free ; the inter- 

 nal organization is unknown, owing to its minuteness, and 

 green matter within. 



170. Tessararthra moniliformis is green; two, three. 



