TRIBE III. MADREPORACEA. 515 



Cells of the corallum at the summits at least contiguous and angular ; 

 lamellae entire, often very narrow or obsolete. 



GENUS II. SIDEROPORA. BLAINVILLE. 



Favositince furcato-ramosce ; cellis bene stettatis, lamellis sex axi medio 

 conjungen tibus. 



Furcato-ramose ; cells with 6 lamellae meeting at centre in an axis, 

 and forming a star of six rays. 



The Sideroporae form closely branched hemispherical clumps, con- 

 sisting of flattened or nearly cylindrical branches, with obtuse sum- 

 mits. The cell is usually slightly vaulted, and the star within is very 

 regular; often at centre where the lamella? meet, there is a short point 

 forming an axis or columella to the cell, which when broken is seen 

 to be tubular in some species. In many of the Sideroporse the inner 

 half of each ray is quite deep within the cell, and the cell appears 

 therefore six-toothed (sex-dentate). The polyps are simply regular 

 stars of twelve short rays, and usually of some tint of bright green. In 

 the species examined by the author, the tips of the tentacles were a 

 rich green, with the bases brownish. 



This genus is united with Porites by Lamarck and Ehrenberg. 

 It was instituted by Blainville, and named in allusion to the star of 

 the cell, from the Latin sidus, a star. It forms part of Oken's genus 

 Acropora, and includes Schweigger's Stylophora, and Gray's An- 

 thophora. 



Arrangement of the Species. 



*1. S. digitata. *4. S. palmata. 



2. S. elongata. *5. S. mordax. 



3. S. subdigitata. 



1. SIDEROPORA DIGITATA. (Pallas.} Blainvilk. 



S. ramulis, J-J" crassis, raro |", obsolete compressis, scepe paulum 

 tumidis. 



