SELENARIAD^. 79 



of his family Cettariaa, and close to Flustra. It is not to be wondered at, that the 

 striking resemblance borne by some of the more flattened or depressed species to the 

 foraminiferous Orbitulites, should have suggested a relationship between them. No two 

 things, however, as is now well known, are farther apart. 



The most striking peculiarity, perhaps, of the Selenariidse, is the peculiar form and 

 constitution of the polyzoarium. In all other known Polyzoa, except m the case of 

 Cristatetta mucedo, the polyzoary is attached in some way to a foreign base, upon which 

 it is immoveably fixed or rooted. This adhesion is effected in three principal modes. 



1 . By the adhesion to some foreign body of the initial or primordial cell, whence the 

 whole of the rest of the growth arises by repeated gemmation ; the fixing of the poly- 

 zoary, as it increases in size, being assisted by means of corneous fibres or tubes the 

 so-called " radical fibres" of most of the articulated Polyzoa. 



2. By the successive cells creeping along the surface of the foreign base, to which they 

 are individually attached, as in Membranipora, and many other genera. 



3. By means of a strong, rigid, calcareous peduncle, upon which the after-growth is 

 supported like a tree upon its trunk. This mode of adhesion is presented in Eschara, 

 Retepora, and others of the rigid, unarticulated Polyzoa. 



In the Selenariidse, however, no indication is, in most cases, apparent that the poly- 

 zoarium has ever been attached. It never exhibits radical fibres or a calcareous stem, 

 nor, in fact, does any part of the surface show marks of its having been adherent. On 

 the contrary, in perfect recent specimens, the entire surface of both the concave and 

 convex surfaces is covered with a continuous chitinous epidermis. 



Other considerations, moreover, would lead to the supposition that, at any rate, some 

 of the Selenariidse enjoy, to a certain extent, the power of locomotion, and which faculty, 

 it may be remarked, is not singular in them, since there is no doubt that the curious 

 fresh-water Polyzoon above noticed Cristatella mucedo is capable of creeping about on 

 the surface of aquatic plants, by means of the fleshy under surface of its polyzoarium. 

 But locomotion in the Seleuariidse, if any possess it, must be effected in a different way. 

 A peculiar attribute of the whole family, almost without exception, is the possession of 

 powerful vibracular organs, which in several species, as for instance in L. Capulus, B., and 

 L. yibbosus, B., have the setae so formed, as apparently to be well adapted for employment 

 as agents in locomotion. In other species, however, as in C. Lowei and canariensis, and 

 perhaps in all the other Cupularits, the vibraculum would appear to be more especially 

 adapted to its usual function, viz., that of a defensive or cleansing organ. Whilst in the 

 curious Selenaria maculata, B., the extraordinary conformation of the seta, which closely 

 resembles in outward aspect the curling proboscis of a Butterfly, leaves its function 

 very obscure. 



When it is stated that the polyzoarium in the Selenariidse is unattached permanently 

 to foreign bodies, it should be remarked that in very many cases a particle of coarse sand, 

 or fragment of shell, or, it may be, a fragment of a dead polyzoary of the same species, 



