Bacillaria.] THE INFUSORIA. 189 



together, resembling a fringe around the lorica. Found in 

 flint. Size 1 -280th. 



180. XANTHIDIUM tubiferum. The tubular spined 

 Xanthidium has long capitated spines. Found in flint. 

 Size 1 -400th. 



Genus L. ABTHRODESMUS. The animalcules com- 

 prised in this genus are distinguished by being free (no 

 pedicle being present), and in having a simple univalved 

 compressed lorica; they multiply by spontaneous self- 

 division, in the form of tables, or compressed and articu- 

 lated ribbons, each animalcule being contiguous to its 

 neighbour. No locomotion or opening to the lorica has 

 been seen. The chief animal character is self- division, and 

 their close alliance, through Micrasterias and Euastrum, to 

 Navicula, rather than to any known plant. The internal 

 green colouring matter of their parchment-like lorica 

 consists of minute homogeneous granules resembling ova, 

 each cell-like lorica containing from one to three bright 

 bodies, analogous to fecundating glands, which are often 

 accompanied with crystalline vesicles, like polygastric 

 stomachs. 



181. ARTHRODESMUS quadricaudatus. The four-tailed 

 Arthrodesmus has an oblong lorica 5 in consequence of 

 incomplete self-division from four to eight are often con- 

 nected together in a straight chain or polypi-like mass ; 

 when fully developed, the lorica at each end has two 

 spines ; these are wanting in young specimens. In some 

 cases, though rarely, the central lorica has horns, and 

 sometimes the terminal ones have a single horn protruding 

 from their middle ; the length of the horns vary ; they are 

 occasionally twice the length of the lorica. The green 



