

TRIBE I. ASTUTE ACE A. 201 



ally grow in symmetrical hemispheres, often of large size. Six feet is 

 a common size, and twenty feet is sometimes met with. The whole 

 surface of these domes, as seen about the living reefs, is a continuous 

 cluster of polyp-flowers. In some species each polyp or flower has a 

 bright emerald centre, bordered by rays or tentacles of purple ; in 

 others the whole polyp is bright purple, or some shade of red, yellow, 

 or brown. The prevailing colours are copper arid emerald green, 

 bright purple, deep brown, purplish-brown, and a reddish, yellowish, 

 or dark umber, with intermediate tints. Some shade of umber usually 

 characterizes the live coral, when unexpanded. A single species was 

 observed with strongly spinous or echinate lamellse (A. echinata), 

 which appeared to have no tentacles, except the elevated fleshy points 

 covering the spines ; it is an instance of secretion of lime by the ten- 

 tacles, and the production of spines or slender teeth by this process. 



The most important characters distinguishing the Astraeas, are, 

 their mode of growth (H 76 to 79); their massive forms; their concave 

 multiradiate cells covering uniformly the whole surface, the rays of 

 which are prolonged out of the cells so as to striate the interstitial 

 spaces though interrupted near half way across ; and the many 

 transverse dissepiments which unite the lamellae by their lateral sur- 

 faces to one another. These dissepiments, when oblique and very 

 numerous, subdivide the cellules of the star, seen in a transverse sec- 

 tion, as shown in figures 4c, 4d, plate 11; but when nearly horizontal 

 or less crowded, they are hardly apparent, except in a vertical section 

 (figures 2 a, 2b, plate 10). This character of the transverse sections 

 is important in the description of these corals, and when the cellules 

 are subdivided they will be described as decompound ; and otherwise 

 as simple. The cells are either wholly immersed, or they stand a little 

 prominent, with the intervening ridges more or less deeply sulcate 

 instead of entire. They vary much in depth in different species, in 

 some the depth exceeding the diameter, while in others it is much 

 less.* In many, a number of prominent points encircles the porous 

 bottom of the cell, forming a kind of corona. The points are appen- 

 dages or teeth to the larger lamella? ; and cells characterized by them 

 are described as coronate within. 



In a transverse section of a corallum, as shown in figure 1 c, 



* We may use the term profundior, quite deep, when the depth exceeds the diameter ; 

 profunda, deep, when the depth about equals the diameter ; sub-prqfunda, or viz pro- 

 funda, rather deep, when less than the diameter, but more than half the same ; and 

 paulo profunda, s/iallow, when half the breadth or less. 



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