Desmidiece.l infusorial ANiMALcuLEg. 257 



Animalcules, are theii' "being free (devoid of pedicle or stalk) and 

 haviBg a simple univalvcd lorica, of a globidar form, surrounded with 

 spines. They are found either single, in pairs, or groups of four. 

 Ehrcnbcrg thinks they may sometimes be developed in the form of a 

 chain. The lorica is cleai', like glass or parchment, covered with 

 simple or branched bristle-like spines. No apertures have been dis- 

 covered in the lorica, nor has any locomotive ox'gan 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 character of the animal nature of this genus 

 is its self-division" 



All the species (as understood by Ehrenberg, see p. 260), have 

 been found in a fossil state in flints. In some sections, which I cut 

 in 1834, they were very abundant, but until Elirenberg's obser- 

 vations on them were known, they were not identified with recent 

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



XAKTHinruM diffonm, (Ehr.) := Ankistrodesmus falcatus, (Ralfs.) 

 Mr. Kalfs has arranged this genus as follows: — 

 * Spines divided at the apex. 



X. armatum. — Segments broadest at the base ; spines short, stout, 

 terminated by three or more diverging points. Comparatively large ; 

 a deep linear constriction on each side. The central protuberances 

 are cylindrical, truncate, and bordered by pearly granules. Empty 

 frond minutely pimctate. End view elliptic. Length 1 -180th. Not 

 uncommon at the bottom of shallow pools. 

 *■ Spines subulate. 



X. aculeatum (Ehi-.) — Spines subulate, more or less scattered, 

 centi-al projections trimcate, obscurely dentate, with a border of 

 pearly granules. (Fig. 109.) This species is distinguished from all 

 the following, by having its spines more or less scattered. Length 

 l-384th to l-377th. Breadth l-393rd to l-347th. 



X. Brebissonii = X. bisenarium (Ehr.) — Spines subulate, marginal, 

 geminate ; central projection somewhat truncate, and margined with 

 pearly granules. 



Var. {b) varians. — Segments broader and more irregular; spines 

 somewhat irregular and unequal. The number of spines is variable 

 Length l-4I6th. Breadth l-408th. 



