IN THE MUD OV THE LEVANT. 39 



reous portion of the animal, than the shell of a 

 mollusk has with the mantle by which it is 

 secreted ; at the same time it is a distinct skin, 

 and more dense than the tissues which it encloses. 

 The skin is unconnected with the calcareous por- 

 tion, for, in drying, it often shrinks away from it 

 into half its original compass, within the calcareous 

 cell, the point of concentration being the inner 

 margin of the spire, where it is fixed by the small 

 necks passing through the adjoining septa. I 

 possess a magnificent fossil illustration of this in 

 a flint, from Flamborough Head, where the animal 

 membrane is of such a diff'erent colour to the 

 silicified shell, that the forms of both are stereo- 

 typed with exquisite beauty. This specimen shows 

 a larare interval between the outer walls of each 

 cell, and the membrane by which it was originally 

 lined ; reminding one of the way in which the soft 

 portions of Entoraostraca shrink, when dried, 

 towards the dorsal portion of their transparent 

 cases. At the same time this membrane is firmer 

 in its texture than the soft parts which it invests. 

 On drying decalcified recent specimens, in order to 

 mount them in Canada balsam, each little bag or 

 segment is found to contain a large air globule, 

 showing that, though the membrane shrinks up 



