on the Organic Composition of Chalk and Chalk Marl. ^^T 



of the shells of Rotalia from the sand of Rimini, of the shells 

 of Penc) oplis planatiis, Pavonina Antillarum, and of Orbicu- 

 lina mimismalis from the sea-sand of St. Domingo, as well as 

 of other shells with their animals from the sand of the Red Sea 

 and the Mediterranean; so that now a view is obtained of the 

 more general organization of the principal groups of the Po- 

 lythalamia. 



It results clearly from what has been said in respect of these 

 species, which are so common and widely distributed, and which 

 have hitherto been designated in systems as small Nautili, that 

 the straight-jointed shells of Nodosaria (formerly viewed as 

 Orthocera), as well as the spiral shells of Rotalia, Cristellaria, 

 &c. (considered as Nautili or Ammonites), and the shells of 

 Biloculina resembling vermiform tubes [Serpula), are none of 

 them internal calcareous parts which were encased by an ani- 

 mal body, similar to the internal bone of Sepia, or the cylin- 

 drical spiral bone of Spirula ; but, on the contrary, that they 

 are external calcareous shells, bearing analogy to those of 

 Mollusks, or more correctly to those of Flustra and Cellepora, 

 which, after separation by an acid, disclose and render visibly 

 free the internal simple body or the Polypary, exhibiting pre- 

 cisely the same form. If the shell of Polythalamia be fre- 

 quently perforated with pores, this is no proof that no other 

 openings exist, or that the animals receive nourishment through 

 many tubes, for the same structure is not unfrequently found 

 in Flustra accompanied with the peculiar opening from which 

 the fore-part of the animal body may be protruded ; and in 

 these exist also fringe-like filaments, which are extensile and 

 retractile, and by no means to be compared to the pseudopo- 

 dia or variable feet of Amoeba, but probably bear analogy to 

 the mantle fringes of many Mollusks, applicable to the pur- 

 poses of creeping and attachment, and for which perhaps they 

 were specially designed. Moreover, Flustra possess a distinct 

 large animal organization ; and the siliceous Infusoria, and 

 probable eggs found in Polythalamia, clearly bespeak in them 

 also similar relations, the discovery of which, however, had 

 hitherto been prevented by the calcareous encasement and the 

 minuteness of the objects. 



It has resulted from the examination of the soft small ani- 

 mal bodies of living Polythalamia, that while many resemble 

 Flustra or Eschara assembled in families or polyparies, each 

 such family being often composed of hundreds of much mi- 

 nuter single animalcules, many others are single animals after 

 the manner of Mollusks. Hence arise external characters and 

 forms which have often a reference to very difTerent relations, 

 wliich it is first necessary to distinguish before we can succeed 



