ASTEOCCEXI^ OF THE SUTTON 8T0XE. 107 



septa, six uniting with the columella ; (3) 14 septa, one half reaching 

 the columella ; (4) 8 septa, all long ; (5) 10 long septa ; (6) 5 long 

 and 5 short ; (7) 12 septa, but the fossilization prevents the short 

 ones being separated from the long. 



No cyclical arrangement of septa exists, and in no instance is 

 there more than one short septum between two longer ones. 



The costse are of the same width as the septa, and usually pass 

 between the costse of the adjoining corallites and reach over the 

 walls of the neighbouring corallites. 



Unfortunately the specimen is too low to have a section made ; 

 but Mr. JS'ewton was good enough to have a part of the calicular 

 surface ground and polished. The polished surface is not very 

 satisfactory, but there is enough to be seen to show that the trans- 

 verse sections of the corallites are mostly polygonal in outline, 

 and that the walls of contiguous corallites are simply united with- 

 out there being any coenenchj-ma between them. The combined 

 walls of neighbouring corallites vary in thickness, and it may be 

 one quarter or one third or one half of the diameter of the lumen of 

 a coraUite, so that the thickness of one wall is not great. The shape 

 of the lumen of a corallite in transverse section is more polygonal 

 than circular, and the diameter varies. The condition of fossilization 

 interferes with the comprehension of the septal development in most 

 corallites ; but it would appear that there is great variety in the septal 

 number. In all the corallites, when there are large and small septa, 

 the latter are single and not in numbers between two long ones. The 

 short septa are either straight or curved towards the larger. There 

 is 'no cyclical arrangement and, except in one corallite, which is 

 very badly preserved, there is no instance of more than twenty 

 septa. In this particular corallite the costoe only are seen, and they 

 indicate the presence of 24 septa. In other corallites eighteen is a 

 common number, of which eight are small and short, the others 

 reaching the- columella. Eight long septa with four short ones is 

 a common combination, and there is still no perfect alternation of long 

 and short septa, the short ones being between four pairs of long ones 

 only. In another instance there are nine long septa, and one not 

 quite long enough to reach the columella ; besides these there are 

 seven small septa, and three pairs of long ones have no septa between 

 them. 



It is evident that all the septa of the calices are not preserved at 

 the free surface of the specimen, for the rubbed-down surface shows 

 sections of corallites with more numerous septa than in the calices ; 

 but the number is not in excess of twenty-four. 



The costal markings in the section show that the costce are con- 

 tinuous with the septa, that the costse of one coraUite alternate with 

 those of its neighbours and reach over the united walls to come close 

 to the lumen. The length of the costae is in relation with the width 

 of the united walls. The costas are more distinct and longer than they 

 are in A. gihhosa. The gemmation of A. plana takes place within 

 and close to the calicular margin. 



The figure given in Quart. Journ. Geol. Soc. vol. xl. plate xix. 



