238 Dr Ckjldstream's Additio7is to the 



tions of the alkalies. Its general appearance may be compared 

 to that of the cases of Tubularia indivisa^ except in point of 

 colour. 



The case thus formed by the old shell and the homy mem- 

 brane, and covered by the Actinea, I have always found inha- 

 bited by a variety of the hermit-crab (Pagurus benhardtis), dif- 

 fering from the common one in having the distal extremities of 

 the hands nearly smooth, and the margins of all the legs fringed 

 with hairs. The crab is so imperfectly covered by the case, that 

 the whole anterior half of the thorax remains exposed, even 

 when the animal retires within it as noiuch as possible. 



This curious combination of animals occurred to me several 

 times in Rothesay and Kames Bays, in Bute, either thrown 

 ashore after easterly gales, or drawn in by flounder-nets. Its 

 natural history is perhaps doubtful. Is the horny case secreted 

 by the Actinea ? Or is it the dead axis of some zoophyte, like 

 that which covers old Buccina (Alct/onium echinatum, FL), and 

 Avhich I have found forming an extension of the body-whorl of 

 the Turbo littoreus, also inhabited by the Pagurus ? Or, is it 

 likely that the old shell, with a young crab in it, may have been 

 swallowed by the Actinea ; that the crab may have forced its 

 way through the walls of the stomach, and the integuments of 

 the latter, and that, the Actinea then secreting a peculiar mem- 

 brane to defend its base, the crab may have found itself provid- 

 ed with a habitation suited to its wants ? To this last supposi- 

 tion an objection is found in the fact, that the full grown shell 

 of Trochus Magus forms sometimes the base of the horny case, 

 and this shell is too large to enter the mouth of the Actinea. It 

 seems to me probable that the horny membrane is produced by 

 the Actinea ; and that its formation presents a striking instance 

 of the operation of that beautiful law of Nature which makes the 

 habits of one animal subservient to the wants of another *. 



Asterias irregularis, (Flem. Brit. An. 486). — Diameter, in- 

 cluding the rays, 3J inches ; colour of the dorsal surface ver- 

 milion-red, with yellowish-white spots ; tips of the rays white ; 



" British zoologists will feel indebted lo Dr Coldstream for his descrip- 

 tion and figure of this, the most interesting of the Actinea tribe ; if indeed 

 this curious creature is really a true Accinea. We shall, in this Number of 

 the Journal, make further mention of it. — Edit. 



