XANTHIDIA IN FLINT. 



305 



silicified, have been detected unmineralized in the chalk, and 

 as flexible as the soft parts of the rotalias.* 



The fossil Xanthidia, (the true nature of which is, 

 I think, still problematical,) are hollow globular or spherical 

 bodies, beset with spines or tubular processes, which, in 

 many species, are fimbriated at the extremities, and vary 

 considerably in number and length. Some species {Lign. 

 53), have these appendages very long, and their extremities 



patulous and fimbriated. In 

 a rare species (discovered 

 by my son), the spines are 

 short, equal, and relatively 

 thick (Irign. 54, Jig. 5); in 

 others they are interme- 

 diate in length, proportions, 

 and number (as in Lign. 54, 

 Jig. 4, 6). The manner in 

 which these bodies occur in 

 the flint, is shown in the 

 example figured in Lign. 

 54; which is a thin chip 

 containing five Xanthidia, 

 that was broken off at ran- 

 dom from a nodule. The 

 specimen is represented of 

 the natural size in Jig. 1 ; slightly magnified as seen by 

 transmitted light in Jig. 2 ; and under a higher power in 

 Jig. 3 ; the fragment having been previously rendered 

 as transparent as glass by immersion in Canada balsam. 



Lign. 53. — Xanthidium palmatum. 

 (Drawn by Rev. J. B. Reade ; magni- 

 fied 500 diameters.) 



* The Xanthidia were first discovered in this state by Mr. Deane, 

 of Clapham, an able microscopic observer, to whom I am indebted for 

 my choicest specimens of the soft parts of Rotalise. See Philos. 

 Trans. 1846, p. 466. 



