42 BALANOPIIYLLTA. 



The 3^oungest individuals observed have the shape of a truncated 

 cone attached by the base. The wall is quite smooth, imperforate, and 

 the se2:)ta, twelve in number, equal and not quite extending to the 

 centre, where the rudiments oi the columella are already visible. At 

 this stage none of the flimily characters are displayed. The dimensions 

 are then about 2 mm. in diameter at the base, 1.3 at the calicle, and 

 .8 in height. The next step of develojDment is the formation of costee 

 on the upward prolongation of the wall. They first appear in the 

 shape of sharp jooints grouj^ed about tlie origin of the septa. About 

 the same time an opening appears on the border and rather outside of 

 the calicle, opposite each of the secondary septa, which gradually 

 widens inwards, dividing apparently the sejDtum in two. The two bor- 

 ders of that opening become the tertiary septa, the secondary septum 

 is gradually pushed inwards, and is replaced by a new one growing out 

 on the same radius from the wall, and but loosely connected with the 

 joined tertiaries and original secondary. In a vertical section of an 

 adult specimen a row of perforations is seen to extend both on the old 

 and the new part of the secondary septum at the lines of junction with 

 the tertiaries. The interior part of the tertiary septum is now to all 

 intents and j^urposes a palus, and the wdiole arrangement quite similar 

 to that of Deltocyathus, for instance. At this stage the septa are 

 rather exsert and jagged on the edge, and seen in profile the resem- 

 blance with Stephanophyllia is quite striking, not taking the attached 

 condition into consideration. 



As the growth proceeds, the point of junction of tertiaries and sec- 

 ondaries moves farther into the calicle, until it rea(;hes the columella. 

 At this period the older or internal part of the secondary septum has 

 nearly or entirely disappeared, and the same process of growth goes 

 on with the septa of the fourth cycle, which become joined to those of 

 the third. 



One or two specimens show a coalescence of two individuals grow- 

 ing in a crowded position. 



Although this species is generally destitute of epitheca, I hesitate in 

 separating from it a form of which a number of specimens were ob- 

 tained in 68 fathoms oft" the Tortugas. These were almost cylindrical, 

 covered nearly to the calicle by a thin wrinkled epitheca, through which 

 the costce can be distinguished; the calicle contracted. All except a 

 few young ones were dead, and have all the appearance of having l:>een 

 killed by being gradually covered with mud, as the calicle has mostly 

 grown smaller and become stunted until definitively smothered. Hav- 

 ing seen none of this form of a healtliy growth, I am inclined to 

 believe that they belong to BalanopliijUia floridana^ modified by external 

 circumstances. 



