322 THE WONDERS OF GEOLOGY. Lect. IV. 



have been enumerated. The body consists of uniform 

 granules, inclosed in a skin or membrane, having one or 

 more cavities or digestive sacs. These animals appear, 

 in fact, to be merely polypes protected by shells ; some 

 have a single cell ( Orbulina) : others consist of several cells, 

 disposed in a conical or cylindrical direction (Nodosaria). 

 Another family has the shell discoidal like the nautilus, and 

 divided by cells ; these are the polythalamia, properly so 

 called, of which there are many genera, distinguished by 

 peculiarities in the aperture, disposition of the septa or par- 

 titions, and direction of the spire and volutions : to this 

 group belong the Eotalia, Rotalina, Cristellaria, &c. All 

 these forms swarm in infinite multitudes in the present 

 seas, and were not less abundant in the ancient ones. The 

 Nummulites of which we have, already spoken (p. 248), have 

 also living representatives (jiummulina of M. D'Orbigny). 

 The distinguishing character of these shells consists in 

 the numerous perforations by which they are traversed, 

 and which in the living state afforded exit to minute 

 filaments or processes.* 



18. Chalk rotalije. — In the Motalicp, which are the 

 most abundant cretaceous forms, the body of the animal is 

 inclosed within the shell, and occupies all the chambers ; 

 and the perforations, which are numerous, admit of the 

 exsertion of the soft transparent feelers or pseudo-podia, 

 which are the instruments of motion. The shell of the 

 rotalia, therefore, though presenting the general form of 

 that of the nautilus, is essentially different : for in the latter 

 the body of the animal is wholly contained in the outer 

 chamber, and the internal compartments are successively- 

 quitted empty dwellings ; whereas, in the polythalamian, 

 all the cells are filled by the soft parts of the animalcule 

 contemporaneously. When the shell, which is calcareous, 

 is removed by weak hydrochloric acid, the body is exposed, 

 * See Medals of Creation, vol. i. p. 232. 



