TUEBINARIA. 13 



accompanying decay of the basal portions, there are cases which look like a true periodicity 

 in the growth, e. g. in many tabulate forms (see below, on Types of Growth). 



Tlic Poh/i)-cai-ilics or Ca//(7(s.»— Confining ourselves to those points which are cha- 

 racteristic of the genus, we find the calicles separated by an intervening mass of porous 

 ccenenchyma. Into this they may either be sunk, or from it they may project above the 

 surface, in which case they carry up the ccenenchyma with them in various thicknesses, and 

 at varying slopes. These differences are of systematic value, and will be described in the 

 section dealing with the principles of classification adopted in this Catalogue. 



The apertures vary from round to oval, being sometimes almost oblong. There is no 

 very marked differentiation of the septa; although different cycles can occasionally be 

 traced in the slight variations in size, and also in the fact tliat the numbers generally range 

 near some multiple of 6— viz. 12, 18, 24, and further directives are here and there recognis- 

 able. Wlien the aperture is oval or oblong, the septa are usually modified, being shortened 

 and sometimes confluent at the corners. In round calicles, the septa are usually verj' uniform. 



At varying depths in the calicles the septa meet to form a columella, which may rise 

 in tlie base of the calicle as a protuberance free of the septa. It is probable that the 

 formation of this columella is an adaptation for the purpose of strengthening the often 

 thin margin of the corallum, which would be far more fragile if perforated by so large 

 a number of open pits. As the corallum thickens, the polyp-ca-vities have to lengthen to 

 keep pace, if possible, with the rising surface of ccenenchyma. As a rule, in such cases tlie 

 columella grows continuously upwards, but occasionally it is discontinuous (specimens of 

 T. xieltatn). 



The septa within the calicles are not infrequently associated with the ridges on the 

 ccenenchyma, and it is impossible to avoid the conclusion, that at one time these ridges were 

 the developments of true costse. In many calicles the septa show a tendency to twist 

 sprraUy, and in protuberant calicles the ridges of ccenenchyma on their walls, in many cases, 

 show the same. A similar spiral twist can be observed in the costse of protuberant calicles in 

 true Madrepores. 



Bcfimtwn of the genus Turhinaria.—lhiAi-Q^oxaria, developing from a parent axial polyp, 

 round which a ring of buds arise above it, free from the basal epitheca in such a way that the 

 first stage of growth forms a stalked cup or plate, with the polyp-cavities opening on its inner 

 or upper face. Growth is continued by this ring of buds, which bud again in tlieir turn on 

 their outer or under sides, either regularly, in which case the original cup shape may persist, or 

 irregularly, which sooner or later results in the complete obliteration of the original cup. In 

 all the transformations of the corallum, however, the polyp-cavities open on only one side ; 



^ • Dana (' Zoophytes,' p. 72-t) proposed to call the submerged iwlyivcavitics " cells," and the 

 projecting polypcavities " calicles." It seems to me that nothing is gained by having two names for 

 the same thing under different conditions. Ecjccting the term " cell," for obvious reasons, the word 

 calicle is here usod tlnoughout for the polyp-cavity vnth its own immediate wall, whether it be sub- 

 merged or protuberant. 



