204 Zoophytes. 



former species. From a small specimen which came with the others, 

 this coral, in the young state, has a narrow base formed on a straight 

 tube. 



I have not seen either of these kinds of coral shaped like other Cy- 

 athophyllae, with a conical tapering stem, yet from the shape of the 

 star they are evidently allied to that genus, so that perhaps they may 

 belong to the next class of instances, in which the coral or coralloid 

 body is evidently modified by the parasitic animals which form a 

 chamber in its substance, yet take a peculiar form, and appear never 

 to be found except in conjunction with the parasite. 



A very common instance of this kind is often to be observed on our 

 own coast. Many of the shells taken possession of by the common 

 hermit crab, are covered with a species of Alcyonium, described by 

 Dr. Johnston of Berwick under the name of Alcyonium echinatum. 

 This Alcyonium gradually enlarges, and being moulded on the body of 

 the hermit crab, forms for that animal a house, adapted to its growth, 

 so that it has no necessity either to enlarge its house by the absorp- 

 tion of part of the cavity of the shell which it inhabits, or by leaving 

 the shell and seeking for another better adapted to its size, as other 

 specimens are obliged to do which have not the assistance of the 

 coral. One can understand that the crab may have the instinct to 

 search for shells on which the coral has begun to grow ; but this will 

 scarcely explain why we never find the coral except on shells in which 

 hermit crabs have taken up their residence. 



The " calthrops shell," as it has been called (Turbo madreporoides. 

 Burrows' ' Elements of Conchology,' t. 27, f. 1), is a shell inhabited by 

 a Pagurus, which is covered by a peculiar species of cellepore. An- 

 other shell, similarly covered with another species of cellepore, is fi- 

 gured by Lister, (Conch, t. 585, lower right hand figure). Both the 

 Cellepora Calthrops and C. Listeri above cited, are peculiar for having 

 the mass of the coral marked with large green spots: and I have 

 several other examples of the same kind from different parts of the 

 world, two species of shells from the Chinese seas, covered with an 

 Alcyonium, each with branching arms, the arms of the two specimens 

 taking different and definite directions. Another, which appears to be 

 very common on the west coast of Africa, is covered with a Lobularia ? 

 with large polypes, all the specimens having four large thick claw-like 

 branches, bending down towards the mouth of the cavity which is 

 inhabited by the Pagurus. 



The Mollusca and Annelides which live in coral, equally cause the 

 coral animals to protect them ; some, as the Modiolae, being sunk into 



