with Descriptions of new Species. 409 



some cells will be found to be furnished with them, while others 

 are destitute of them. An occasional opacity of the walls of 

 the cells of a species usually transparent, is certainly sometimes 

 produced by age, but it is a rare effect, and the number ofLe- 

 pralia with transparent cells is not great, and the other charac- 

 ters of the species still remain unaffected. It may be doubted 

 how far the examination of a number of specimens of a species 

 is necessary for the purpose of ascertaining the effects of age 

 upon it, and whether one well-developed specimen would not 

 furnish all the information to be acquired on this point, see- 

 ing that it presents examples of both young and aged cells, 

 those in the centre from the circular development of most of 

 the species of the genus being the aged ones, and those near 

 the circumference of the crust being of course the most re- 

 cently formed; and yet how httle difference do we find be- 

 tween the central and circumferential cells ! the former are, 

 indeed, sometimes provided with opercula not present in the 

 latter. 



The changes produced in the Leprali(£ by age, therefore, are 

 not numerous, nor are they such as would be likely to lead to 

 errors in the discrimination of species ; although candour re- 

 quires the confession that I ^^ as once imposed upon by the 

 altered aspect of a species, L, hyalina, arising from the opa- 

 city of the cells, which are generally transparent, and v, as led 

 to regard it as a distinct species. This however, I feel assured, 

 would not have occurred, had I at the time command of even 

 a tolerable microscope. Thus my Lepralia cylindrica is no- 

 thing more than a peculiar condition of L. hyalina. 



Thirdly, what are the alterations occasioned in the appear- 

 ance of Lepralue produced by diying ? 



An alteration of colour is one: most Leprali(E in a recent state 

 are of a reddish colour, the tint varying with the species ; this is 

 in a great measure lost by drying, the specimens becoming more 

 or less colourless. A second is, that the perforations contained 

 in the walls of the cells of some species, visible in the Lepralia 

 just removed from its native element, become more manifest 

 and more defined, but still present in each species the appear- 

 ances of size and form which are peculiar to that species ; and 

 as most LepralicB are figured and described from dried ex- 

 amples, they ai'c therefore upon an equality in this respect, 

 all having undergone the same process. 



Fourthly, with regard to injury. The Leprafue are subject 

 to injury and mutilation arising from several causes ; thus they 

 may be injured by the action of the waves while still attached 

 to the objects upon which they grow, by the trituration of" the 

 shells and fuci on which they are placed upon each other as 



Ann. ^- Mag. N. Hist. Vol. ix. 2 E 



