IK SOME SEEIAL COBALLA. 363 



largely fixed by its base, the common plateau being covered with 

 a thin but complete epitheca. The columella is parietal and 

 reduced to a few trabeculse derived from the inner edge of the 

 septa. In the specific diagnosis they state that the horizontal 

 section shows no columella, and that the union of the corallites 

 is by thin and linear walls. 



It is best to examine the walls between the serial corallites 

 first, and then to proceed to the examination of the basal structure. 

 A vertical fracture indicates that there is no true wall between 

 the serial corallites, and the septa are very exsert, standing up 

 far above what, from its position, seems to be the top of a wall. 

 Eeally this top is the upper surface of a nodule, circular in vertical 

 fracture, which extends from one septum to another in the place 

 of a wall. It is the top nodule of a vertical series standing out from 

 the flanks of opposed septa ; and one nodule is separated from 

 those above and below it by some space, where there is no trace 

 of intercorallite wall. This space is occupied by arched dissepi- 

 ments ; so that instead of a solid continuous vertical wall between 

 neighbouring corallites (series), there is a vertical series o£ nodular 

 processes with endotheca filling up the spaces between them. 

 It is this endotheca which, prevents one visceral cavity communi- 

 cating with those on eitlier side as in the Perforata. 



The columella is formed of stout processes from the septal 

 ends, and besides by a growth which commences at the base ; it 

 is therefore partly parietal and partly essential, and is always 

 trabeculate. 



On examining the base of the corallum, no true theca is found, 

 so the " plateau commun " appears to be a mythical structure. 

 There is a stout epitheca inseparable from any thing else ; and it 

 occupies the position of the basal wall, and the septa and colu- 

 mella arise from it. It is very thin but strong, is marked with 

 concentric ridges and lines, as is usual to epitheca ; and it clearly 

 bounds tlie interseptal spaces below. 



The nodular processes of the interserial or intercorallite wall 

 cannot be mistaken for synapticula ; they are in the line of where 

 a wall might be, and are septal structures. They are. however, 

 very remarkable. 



This species certainly departs from the generic characters of 

 the CoeloricB. The well-known mural perforations of Coeloria 

 d<iedal(jBa^ Solander, sp., are close to the margin, and are due to 

 imperfect growth ; they in no wise resemble the condition in the 



LINN. JOUEN. — ZOOLOGY, VOL. XVII. 2S 



