B4 Br. G. A. Mantell on the Animalculites of the 



before this Society (but not published), the dark veins and mark- 

 ings in the pillars of Purbeck marble in the Temple Church, 

 are attributable to the remains of the soft bodies of the fresh- 

 water shells of which that limestone is composed, in the state of 

 molluskite. 



I have stated my conviction that the experienced microscopical 

 observer will not hesitate to agree with me in the opinion, that 

 in- the fossils before us we have the mineralized soft bodies of 

 polythalamia j and I have obtained, through the kindness of 

 Mr. Williamson of Manchester, a recent object for comparison, 

 which is perfectly analogous, not to say identical, with the best- 

 preserved flint specimen. It is the body of a Rotalia from which 

 the shell is removed, and is associated with other polythalamia, 

 &c.; it was obtained with numerous other interesting recent or- 

 ganisms in sediment from the Levant. 



Infusoria in Flint : — Xanthidia. — Our flints contain abundance 

 of several kinds of infusoria ; as for example, various species of 

 the genera Pyxidicula, Peridinium and Xanthidium. 1 shall re- 

 strict my remarks to the last-named animalculites, which, from 

 their elegant forms and good state of preservation, are highly in- 

 teresting to microscopic observers. The Xanthidia are minute, 

 globular or spherical bodies (from ^^^o^h to j^^th of an inch in 

 diameter), beset with tubular processes, which terminate either 

 in fimbriated or acuminated extremities. They are stated by 

 Ehrenberg to be siliceous, and to be analogous, and some of the 

 species identical, with living forms which abound in boggy pools 

 and ponds. Several of the recent kinds occur in the ponds on 

 Clapham Common, Hampstead Heath, and other places around 

 London. These organisms are however considered by the most 

 eminent botanists not to belong to the animal kingdom, but to 

 be vegetable structures, related to the Desmidiacece ; and are 

 defined as plants having " fronds simple, constricted in the mid- 

 dle ; segments slightly compressed, turgid, reniform or orbicular 

 and entire ; their surfaces more or less furnished with simple or 

 branched elongated spines, either scattered over the surface or 

 confined to the margin, where they are placed in two rows, one 

 on each side the marginal line*.^^ Ehrenberg, on the other hand, 

 describes the Xanthidia as animals having spontaneous motion 

 and increasing by self-division. But I must not dwell on this 

 important and difiicult question ; the arguments on both sides 

 are concisely stated in ^ Annals of Nat. Hist.^ March 1845, p. 188, 

 to which I would refer those who are interested in the subject. 

 I do not presume to think that my opinion on this problem is 

 of any value ; but waving the question of the animal or vegetable 



* See Mr. Ralfs's paper on the Desmidiac^ee, Ann. Nat. Hist. Jan. 1845. 



