MATTHAI— RECENT COLONIAL ASTR^ID^ 



flat, rough or smooth, vesicular, celkilar or dense, the extent to which the spaces between 

 the thecse were filled with calcareous deposit) ; (3) the flat or arched chai^acter of the 

 dissepiments ; (4) the presence or absence of an epitheca ; (5) the character of the theca 

 (visible or sunk in the peritheca, its comparative thickness) ; (6) the number of septal 

 cycles and of the septa constituting each cycle ; (7) the nature of the septa (oblique or 

 perpendicular, narrow or broad, exsert or not, presence or absence of teeth on their 

 margins, sides rough or smooth) ; (8) the presence or absence of paliform lobes* and their 

 shape, size and surface characters ; (9) the nature of the costge (present or absent, visible 

 or sunk in the peritheca, rough or smooth, thick or thin) ; (10) the nature of the 

 columella t, and the presence or absence of upright rods upon it. 



None of these characters were found to have any constant value, and therefore the 

 distinctions based on them would appear to be arbitrary. Not only wei'e there gradational 

 stages connecting genera like Orhicella, Favia and Prionastrea, and connecting species of 

 the same genus, but in many single large specimens the skeletal characters varied to such 

 an extent that pieces cut off" from different parts, if regarded separately, had to be 

 relegated to different species. The descriptions of many coral species have, in this manner, 

 been taken from isolated specimens, hence the enormous multiplication of synonymy in the 

 Madreporaria. 



Much attention has been paid by various authors to the epitheca. Its origin is still 

 obscure. Von Koch, from his study of the development of Astroides ccdycidaris (78), 

 regarded it as the continuation of the basal plate, and, as is evident from his figure (fig. 4), 

 a secretion by the ectoderm of the column-wall where it passes into the base or foot. It 

 would therefore be similar in origin to von Holder's eutheca (64). Bourne (12, pp. 36 — 39), 

 on the other hand, defined the epitheca as formed "from the free edge of the soft tissues 

 on the exterior of the corallum, as they retreat farther and farther from the original surface 

 of attachment," hence similar in origin to the peritheca]: deposited between the corallites. 

 Indeed— and in this I am inclined to agree with him — he regards the exotheca, peritheca, 

 coenenchyme and epitheca as homologous structures, differences, if there be any, depending 

 on quantity and texture. Lacaze Duthiers (60, p. 225) also was doubtful about the true 

 nature of the epitheca and how to determine its presence or absence. With reference to 



* True pali, arising from the basal plate and situated between the columellije and septa, have not been 

 seen in any of the Astrseids I have examined. 



t Prom the sections of the coralla it is not possible to determine if true columellse, viz. rods arising 

 from the basal plate and formed in folds of the basal disc of the polyps, are present in Astrseids. The 

 so-called " dark centres " are no test as they are seen in all the columellar parts, even in some undoubted 

 septal trabeculse which have united with and formed part of the columellse. 



+ I use this term as Professor Gardiner defined it in his paper on Cosnopsammia, viz., "That part of 

 the corallum of colonial madreporaria which is deposited outside and subsequently to the theca." Bourne 

 (13, p. 217) in a subsequent paper modified the strong views he had at first held on the subject of the epitheca 

 and reverted to von Koch's original contention in these words : " ...I may give my adherence to von Koch's 

 definition of epitheca, that it is a more or less conspicuous offset of the basal plate, which lies on the outer side 

 of the body-wall, but no longer forms a part of the surface of attachment, and in the majority of corals has the 

 form of an investment of the column (die Gestalt eines Kegelmantels). As such it is readily recognisable in 

 the anthoblast of Fungia, and in some cases 1 have been able to detect traces of an analogous structure in the 

 anthocyathus (fig. 16, ep.)." 



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