Mr. A. H. HassalPs Catalogue of Irish Zoophytes. 173 



Dr. Johnston, to whom I wrote respecting this zoophyte, refers 

 me to a figure in which the cells are shaped as in mine, given in 

 Ellis's work (Plate xxiii. fig. D.), and suggests the possibility of 

 Ellis having found the two forms of cells, viz. the rhomboidal and 

 the rounded, upon one and the same species. This communication 

 led me to make a careful examination of numerous specimens of F. 

 salicornia, the results of which has been such as I had anticipated. 

 In no one instance have I ever detected the two forms of cells upon 

 one and the same portion, but have always found the differences 

 which I have pointed out to be constant between specimens. Ellis's 

 figure proves that he had seen my species ; but it is also evident that 

 he overlooked the material points of difference between it and the 

 ordinary kind, an unusual error for him to commit, I acknowledge ; 

 but nevertheless possible. The circumstance of his having given 

 two separate figures of Farcimia is in favour of my opinion of their 

 distinctness as species. 



There is one general and undeviating principle presiding over the 

 form and arrangement of the cells of all cellular zoophytes, and ope- 

 rating with such mathematical precision as to give to each species a 

 certain type or character by which it may be distinguished from all 

 others, each having cells of but one shape, and arranged in a uniform 

 and determined order. To imagine, therefore, the existence of two 

 forms of cells so distinct in their character, upon one and the same 

 species, and constituting a part of it, is to suppose an anomaly, of 

 which I believe the whole range of zoophytical productions does not 

 furnish a single example. The differences between the two species 

 are not such as can be explained by a reference to any adventitious 

 causes, such as exposure, the mode of drying, &c. ; they are not those 

 arising from mere magnitude ; in a word, they are structural. 



Alcyonidula 

 Alcyonidium. 

 Alcyonidium hirsutum. — Dublin bay ; not common. 

 A. echinatum. — Dublin and Killiney bays ; common. 

 A. parasiticum. — Dublin and Killiney bays; frequent. 



Melobesia. 



Melobesia elegans. This beautiful microscopic object, which re- 

 ceived its name from Mr. Bean, is not more than the sixteenth of 

 an inch in diameter. It is composed of numerous plates of irregular 

 form and dimensions ; these plates are inserted into a raised margin 

 or framework, and each is perforated with minute tubular apertures. 

 Whether it is furnished with polypi or not, I believe, is not deter- 

 mined. See Plate VII. fig. 2. 



On Fuci ; Dublin bay. 



Halichondria*. 



Halichondria papillaris, Fleming. Spongiaureus, Solander. 



Common, encrusting fuci ; Dublin and Killiney bays. 



H. palmata. — Dublin bay ; not common. 



* For an account of this genus, see Fleming's 'British Animals.' 



