MISCELLANEOUS. 75 



irregular, and void of symmetry under the microscope. Next, as spreading 

 like a black patch over the pearly inside of shells, the cells when cleansed 

 of impurities are discovered advancing to decay. 



Until we can speak of the origin and progress of increment of a 

 specimen, whereby its mode of enlargement shall be understood, its real 

 formation cannot be satisfactorily elucidated. 



Probably the cell alters soon after the decay of the tenant, whence 

 there cannot be a strict correspondence between the living specimen and 

 the dead. 



Many are found in the interior of bivalves, apparently promising- a 

 long period of security, yet they are rarely surviving'. 



Let us assume, in general, that the Lepralia may be defined an in- 

 vesting, calcareous, cellular scurf. 



(1.) Lepralia pustula. — Plate XXIV. Fig. 1. — If the prolific 

 ovum or the gemmule of the Lepralia could be obtained, we might dis- 

 cover how its original adhesion is effected, and next how the augmenting 

 cells are developed or acquired, and thence ascertain the circular, 

 quadrangular, or irregular figure exhibited in greater maturity. Nearest to 

 this is the selection of some specimen, whose growth to appearance is 

 unrestrained and unobstructed. 



A patch, of what I shall denominate, provisionally, the Lepralia pus- 

 tula, was diffused on the inner surface of an old oyster shell of large dimen- 

 sions. The whole seemed to radiate from a common, perhaps the original 

 centre, and on reaching the circumference, was terminated in several irre- 

 gular curves. — Plate XXIV. fig. 1. The same enlarged, fig. 2. 



The surface of this specimen was composed of half ovoid cells, with a 

 plain semi-elliptical orifice near the summit. A serrated circle, with a 

 small semi-elliptical aperture behind it, begirt the base of each cell. In- 

 tervals separated the cells, which themselves inclined inwards, the orifice 

 being directed towards the centre of the specimen, figs. 2, 3. 



The serrated circle is to be discovered only by a high magnifying 

 power, fig. 4. 



