Bacillaria.] THE INFUSORIA. 187 



in the lorica, nor has any locomotive organ been seen. 

 The green mass of granules in the interior is considered as 

 ova, and the glandular transparent globule observed in the 

 centre of X. aculeatum as a testes. The only determinate 

 and satisfactory character of the animal nature of this genus 

 is its self-division. 



All the species have been found in a fossil state in 

 flints. In some sections, which I cut in 1834, they were 

 very abundant, but until Ehrenberg's observations on 

 them were known, they were not identified with recent 

 species, and then considered as mere defects in the stone. 



173. Xanthidium hirsutum. The hairy Xanihidium is 

 green, of a globose form, and covered with simple hairs. 

 They are found either solitary, or in pairs. Size l-430th. 

 Found in peat-water. A fossil specimen is shewn in 

 plate xii., fig. 512. 



174. Xanthidium aculeatum. The spinous Xanthidium 

 only differs from the preceding in the lorica being covered 

 with short-pointed spines, and occasionally as many as 

 four being connected together. In the engraving, ^/c/e ii., 

 fig. 109, a pair is shown highly magnified. In the middle 



of each globe is one or more large clear spots ; these, as 

 well as the green coloured internal mass, prevent our 

 seeing whether it is further organized. In the fossil speci- 

 mens, so abundant in many flints of the chalk formations, 

 the internal parts have disappeared ; and hence the lorica, 

 with its spines, is seen diaphanous. Size of the single 

 sphere 1 -430th to l-288th. Found with X. hirsutum. 



175. Xanthidium fasciculatum. The clustered- spine 

 Xanthidium has an oblong or globular green body, with 

 long sharp spines, disposed in pairs or clusters. They are 



