RUGOSA. 49 



Order RUGOSA M.-Edw. & II. 



The section of Rugosa was estalilislicd by Milne-Edwards and Haime 

 foi' a largo number of fossil corals, all of an older age than the carbonif- 

 erous formation, and particularly abundant in the pahcozoic ages. Their 

 chief characteristic, according to those authors, is the development of 

 the septa proceeding from four primary ones, whilst in all of the living 

 corals the primary number is six. In addition, the chambers are closed 

 inferiorly by an abundant endotheca, often assuming the shape of floors ; 

 but this character is not found in all the families of the section, though 

 certainly in the greater number. Mr. E,. Luclwig has shown (H. v. 

 Meyer's Pakeoutographica, Vols. X. and XIV.) that the tetrameral 

 arrangement claimed for the Rugosa is only apparent, there being origi- 

 nally^ six jjrimary sejita ; but that the further development in each 

 system is as^inrnetrical, and that two of the systems remain generally 

 undeveloped. 



I had, before having knowledge of Ludwig's researches, come substan- 

 tially to the same conclusions by the examination of Lophophi/llmn pro- 

 liferum Edw. & II., from the carboniferous formation, a form very suitable 

 for that study. As I find my mode of explaining the development 

 slightly different from Ludwig's, it may not be too much out of place to 

 mention it here in a few words. 



When the youngest stage of the coral is examined by cutting through 

 the tip of the conical IjiphophnUimi priJifcnmi^ six ]U'inuuv septa and six 

 interseptal clKuubers are found, placed synnnetrically on two sides of 

 a vertical plane, and un9(|ually developed. This plane would pass 

 through .wo of the primary septa, of which one may be called anterior 

 and the othei- posterior, for convenience merely. The two lateral 

 systems (which would be divided by a plane at right angles to the 

 antero-posteiior plane) are at the earliest stages larger than the others. 

 In progress of growth the anterior primary system is checked in its 

 development, and the two adjacent chambers partly coalesce to form the 

 so-called aeptal fossa. The posterior primarv septum is fully developed, 

 and joins the columella (when there is one). The systems between 

 this and the two adjacent primaries do not become subdivided again, so 

 that these three septa remain close together ; according to Ludwig, 

 they subdivide to a small extent in some genera. Thus, of the six 

 primary interseptal chambers, the two posterior ones remain undivided. 

 The four other ones are each divided by a secondary septum joining the 

 primary ; of the two half-systems thus formed in each, the anterior one 

 is again divided by a tertiary septum joining the secondary ; next the 

 anterior quarter-systems are divided, and so on. The four lateral 



