120 SKETCH OF THE INFUSORIA 



1. Xanthidium? ramosum. Corpuscles globular, separate or binary, 

 spines scattered, terminating in three or more points ^^ to ^V line. 

 Fossil in gun flints. 



2. Xanthidium . (Fig. 15, PI. I.) Binary, each portion 



haring numerous rather long arms terminating in three diverging 

 points. 



This very beautiful American species is, when living, of a fine 

 green color. Its carapace is hard and apparently siliceous, as it 

 retains its form in spite of the action of fire and acids. Every 

 living specimen of this species v^^hich I have seen, has been 

 composed of two symmetrical portions, as shown in the figure. 

 These bodies, when in the position shown in the figm-e, have 

 much resemblance to Ehrenberg's drawings illustrating the spon- 

 taneous division of some of the species. When thrown into 

 other positions, so that the line of union of the two portions is 

 not seen, it may easily be mistaken for a simple spherical body 

 bristling with arms. The t\vo portions often separate after death, 

 and may then be mistaken for individuals resulting from sponta- 

 neous division ; but by throwing them into various positions by 

 means of a compressor, tlie orifice corresponding to the line of 

 separation of the two original parts may always be seen. The 

 same remark will apply to the next species also. 



It occurs not unfrequently in a subalpine pond a few miles 

 from West Point; it is also occasionally found in ditches, in peat 

 bogs, &c. 



3. Xanthidium . (Fig. 16, a, h, PI. I.) Binary, each portion 



somewhat triangular and terminating at each angle in tlnee short, 

 diverging arms, each having tluee small diverging points. 



The smaller size and triangular form of these bodies, make me 

 think them of a different species from the preceding. I have not 

 seen any intermediate forms, although they occur together in 

 about equal abundance at the above-mentioned locality. 



I must here remark, that a transition from Xanthidium to 

 Euastrum appears quite evident, through the binary h'iangular 

 bodies, often having projecting arms, represented in iigurcs 2, 3, 

 4, 9 and 8, PI. I. 



