676 Div. 4. RADIATA.— POLYPI. Class 4. 



granules, that it dries entire on the axis, and retains its colours, which are often very bright and beautiful ; but it 

 is soluble in acids. The Polypi of several species have been examined, and found to have eight toothed tenta, 

 cula, and a stomach and other viscera, like those of CoroUium. 



Among them, M. Lamouroux distinguishes Plexauies, which have the covering membrane thick, with the cells 

 not prominent, and it effervesces but slightly with acids ; Ermicen, which have the same back, but the cells of 

 the polypi prominent ; Mnrisen, which have the covering of moderate thickness, with projecting mammillae covered 

 vf ith rough and imbricated scales ; and Primnoa, in which the mamillae become imbricated by tiie one hanging 

 partially over the other. 



LiTHOPHYTA, 



The second tribe, have a fixed internal axis of stony consistency. The leading genera are, Isis, 

 Madrepora, and Millipora ; but they admit of subdivision. 



Isis, have the axis branched, and no cells or cavities on its surface ; and the internal tunic of gelatinous matter 

 is mixed with calcareous particles, as in Gorgonia. 



Corallhia [Isis 7iobilis of LiniiiEus], is the Coral of commerce, so much admired for its fine red colour, and the 

 high polish of which it is susceptible, and so often made into trinkets. There are very profitable fishings (or 

 divings) for it in different parts of the Mediterranean. The covering is of a reddish colour, and contains cal- 

 careous matter. The polypi have eight toothed arms, or tentiicula. Melita, has the stony axis interrupted by 

 nodes full of a substance of the consistency of cork, his, properly so called, has the horny part knotty ; and 

 the bark thick, soft, and easily removed after death, ilopsia, has the bark much thinner, but also stronger. 



Madrepora (the Madrepores), — 

 Have their stony substance sometimes branched, and sometimes In rounded masses, or in leaves ; but 

 it is alvFays furnished with laminae, concentrated toward points in the form of stars, or terminating in 

 lines more or less serpentine. During life the stony part is enveloped in a horny bark, which is soft 

 and gelatinous, and roughened by rosettes of tentacula, which are the Polypi, or rather tlie Actiniaj, for 

 they have more than one row of tentacula. The laminas of the polypi have some slight resemblance 

 to those on the stony case ; and the covering and polypi contract a little upon being touched. 



The varieties of their general form, and the figures which are produced by the combinations of their laminae, 

 have been made the foundation of numerous subtiivisions ; but several of these run into others, so that they are 

 not absolutely specific, and it will be impossible to fix them definitely until the relations between their forms 

 and the polypi are known. 



Wlien there is only a single star, circular or elongated, with many laminae, they are the Fungia of Lamarck ; 

 and their polype resembles a single Actinea, with numerous t«ntacula ; and the opening of the mouth corresponds 

 exactly with tJre point toward which the laminse converge. 



There are found among fossils stony polypi<lonis consisting of a single star, which appears never to have 

 adhered to others. These are the Turbinata and Cyclolitlnn of Lamarck, and the Turbinolopsis, Lamouroux. 



When the Madrepore is branched, and the stars are confined to the extremities of each branch, it is the Caryo- 

 phyllia of Lamouroux. The branches are striated, and each star answers to a mouth surrounded by many 

 tentacula. 



Oculina, have the small lateral branches very short, which gives them the appearance of having stars along the 

 branches, as well as on the extremities. Madrepora, or Madrepores properly so called, have the whole surface 

 roughened by little stars. Pocillopora, have little stars with pores in the intervals ; and f^erialopora, have their, 

 stars in lines. Astrea, have a broad and generally convex surface, hollowed by crowded stars, each having a 

 polype with numerous tentacula in a single row, in the centre of which is the mouth. Explanaria, are broad, 

 with the stars on one side. Poriles, has the stony substance branched. Meandrina, have the surface formed into 

 little hills and valleys. In each valley there are mouths ; but the tentacula, instead of forming stars or rosettes 

 around them, are range<l along the sides of the valley. In some, however, the mouths are merely festooned. If 

 the hills which separate the valleys are raised into crests furrowed on both sides, they are called P<jfo«Ja; and 

 mouths, usually without tentacula, are found in the valleys, the crests probably acting as substitutes for the latter. 

 There are also others, which have these hills conical or star-shaped, and the principal distinction of them is 

 having the polypi on the projecting parts or in the hollows. Agaricina, are composed of lamiuic, having valleys 

 only on the one side, and the sides of the valleys furrowed. It is probable that we should consider as nearly 

 allied to the Madrepores, certain polyi)idoms composed of cylinders, the sections of which form stars. These are 

 Sarcinula, and when they have a solid axis, they are perhaps nearly allied to Tubipora, in the first family of the 

 order. ^ , 



MlLLIt>ORA, — 



Which compose the third genus, have the stony portion much diversified in shape, and the surface 

 scooped only into small holes or pores, and sometimes there are no apparent perforations. Disticho- 

 pora, have strongly marked pores on two sides of the branches. Millipora proper, are solid and 

 variously branched. Sometimes the pores are not discernible, and they are NuUipores. Eschora, have 

 flattened and leaf-like expansions. Retcpora, are Eschorse pierced like a net-work. Adcona, are 

 Eschora on articulated stems, entire, or pierced like a net-work. 



