78 



leoferum, and pyxidiculum, together with casts of Polythalamia and 

 other bodies frequently found in flints. 



This singular discovery at once suggested the possibility of ascer- 

 taining the true nature of these bodies, as it afforded facility for isolat- 

 ing and mounting them in various ways for examination. From their 

 minuteness, however, it was impossible to examine them chemically, 

 or to apply a powerful solvent without risk of damaging the instrument, 

 while observing its effects upon them. In shape they are somewhat 

 flattened spheres, the greater part of them having a remarkable resem- 

 blance to some gemmules of sponge, and having a circular opening in 

 the centre of one of the flattened sides (Plate IX. figs. 10 and 11). 

 The arms or spines of all appear to be perfectly closed at the ends, even 

 including those which have been considered in the flint specimens to 

 be decidedly tubiferous, showing that if the arms are tubes they could 

 afford no egress to a ciliated apparatus, similar to those existing among 

 zoophytes. On submitting them to pressure in water between two pieces 

 of glass, they were torn asunder laterally like a horny or tough carti- 

 laginous substance, and the arms in immediate contact with the glass 

 were bent. Some specimens put up after several weeks maceration in 

 water, were so flaccid that, as the water in which they were suspended 

 evaporated away, the spines or arms fell inclined to the glass. These 

 circumstances alone seem clearly to disprove the idea of their being 

 purely siliceous. The casts of the Polythalamia, portions of minute 

 crustaceans &c, appeared also to be, like the Xanthidia, some modi- 

 fication of organic matter, and in the case of the Polythalamia, the 

 bodies are so perfectly preserved, that in some the lining membranes 

 of the shells are readily distinguished (figs. 17 — 19). By far the 

 greater number of the specimens of Xanthidia found in flints, are 

 more or less mutilated and crippled ; and it is not a little remarkable 

 that the same state, both as to character and extent of deformity, 

 exists among those in the chalk, and affords strong presumptive evi- 

 dence of the identity of the two objects. During the investigation 

 I had observed many thin, empty shells, somewhat like the husks of 

 peas, more transparent than the Xanthidia, somewhat crumpled, and, 

 with one exception, cracked open laterally. The entire one contained 

 a small globular body, about the size and color of the smallest kind of 

 Xanthidia, but quite smooth.* These I conceived to be identical 

 with the Pyxidicula of the flints. This fact seems to throw a little 

 light on their nature, and taken with the circumstance that a large 



* I have since found reason to believe many of these bodies to be portions of Rotalice. 



