242 REPORT— 1872. 



Committee in adding them to those previously described by MM. Milne-Edwards 

 and Jules Haime. By this addition, the number of British Carboniferous 

 corals amounts to 156 species. 



From the forms which have been recently sliced, and also from those of 

 former years, the Committee have ascertained that among these species from 

 300 to 400 varieties occur, an increase which is so great, and the variations 

 so minute, that it becomes difficult to determine specific characters among 

 these corals. 



The gradations of the varieties are in some cases so constant, and pass 

 so imperceptibly into each other, that they induce the inference that there 

 has been an inherent tendency in the polyp to vary independent of, but to 

 be modified by, the conditions of its surroimdiugs. 



The forms occurring in deposits which have resulted from deep water are 

 not only more symmetrical in outline, but also more perfect in their internal 

 structure than such as are met with in strata formed in shallow water, 

 where they have been exposed to the constant shiftiiigs and abrading influence 

 of shore deposits. 



In the case of such forms as occur in a matrix originally in the state of 

 fine mud, these are small in size ; and they seem to have been gradually 

 exterminated by the impurity of the water, arising from the increase of the 

 fine sedimentary matter originally held in suspension. 



Many of the specimens which have been sliced are found to be perfectly 

 useless from their imperfect state of fossilization. Some reveal structural 

 characters not previously noticed by authors in this branch of Palseontology ; 

 it is desirable that these should be studied further before a complete classi- 

 fication of this group of animal life is attempted. 



The classification of corals has in some instances been based upon external 

 aspects ; in others on the number and form of the septa. The number 

 and arrangement of the lamellfe which pass from the inner margin of the 

 primary septa and fill up the columeUarian space have also been adopted as 

 bases of classification. 



Some writers regard the form and position of the dissepiments of the 

 endotheca as of specific importance ; and some rest generic and specific 

 distinctions upon the presence or absence of the columellarian line which 

 passes from the inferior to the superior, and terminates in the centre of the 

 calice. Observations, however, justify us in inferring that, although these 

 several characters are of importance, they cannot be depended upon for 

 specific determinations. 



During the last fifteen years no less than 10,000 specimens have been 

 sliced, many of which show structural diff'erences" in character from such as 

 have been accepted as of specific importance, which induce us to conclude 

 that further examinations are necessary before determining even a variety. 



It has been stated that the columellarian line has been accepted as of 

 generic value. In a new group of corals, which will form the subject of 

 an extensive memoir, this line is developed, in some instances, near the 

 inferior, and in others it occurs only in the superior portion of the coral. 



The dissepiments filling up the interseptal space are in some forms angular, 

 in others subangular and. rectangular. We have, however, recognized these 

 several outlines in the sa^e form, and cannot, therefore, accept the outline 

 of the dissepiments as of specific importance. 



In the case of the number of lamelke also, some forms present the lamellae 

 in one part, while in another part of the same coral the space is filled up 

 by tubulsB. 



