262 W. H. SHERZEB THE GENUS CHONOPHYLLVM. 



growing vertically 40 mm has gained but two new septa. In some forms, 

 however, a greater number of new ones are introduced showing the 

 tetrameral structure and pinnate arrangement along the cardinal septum, 

 apparently following the law of Dr. Kunth. Others are introduced 

 irregularly, however, throughout the quadrants without regard for any 

 established statutes. 



Dissepiments. — A well developed vesicular structure occurs in the outer, 

 narrow, interseptal cavities as first pointed out by Rominger. These vesi- 

 cles are generally delicate and rendered more or less irregular 1 >y the intro- 

 duction of larger ones, probably produced by the union of neighboring 

 septal layers (figure 4). In general they are formed by narrow bands, 

 united along their edges to opposite septal faces, convex upward and 

 superposed in such a way as to cut off the greatest amount of space with 

 the least expenditure of material. In this we have a clue to the use of 

 these structures. As the growth of the polyp demanded more commodi- 

 ous quarters, a gradually expanding corallum was constructed. The 

 lower, unoccupied portions, now entirely useless, had to be shut off from 

 that which was habitable by ectodermal secretions of calcium carbonate. 

 This was accomplished in three ways among the Paleozoic corals : (1) 

 by vesicles alone, (2) by tabulae alone, or (3) by a combination of vesicles 

 and incomplete tabula 1 . In the case of Chonophyllum, vesicles were 

 deposited in the outer area and in the central area irregular transverse 

 leaflets which represent rudimentary tabulae. In the case of polyps 

 which early matured and then continued to build a long cylindrical 

 corallum, as in Zaphrentis gigantea, etc. there may lie needed some such 

 explanation as that given by VerrilL* 



In the outer area these vesicles tilled the interseptal cavities to within 

 one or two mm of the surface of the septa, but about the pit they were 

 left more open, allowing the thin septa to project with their granulated 

 surfaces. 



Central Area. — As has previously been stated, the primary septa reach 

 the center as double lamellar plates, where they may be more or less 

 twisted, but not so as to form a columella. Vertical sections through 

 this region show the septa as angularly wavy, vertical lines. In the 

 vicinity of the pit the vesicles become more irregular and elongated, 

 and the plates forming them pass into irregular transverse leaflets. No 

 true tabula? are to be found in any of the species, although when these 

 leaflets occur at approximately the same level in adjoining wedge- 

 shaped cavities between the septa they, for short distances, may simu- 

 late irregular tabulae. A patch of this central area is shown in the lower 

 portion of figure 5 (plate 8) ; although small, it is entirely characteristic. 



* Am. Jonrn. Soi., 3d series, vol. iii. 1872, i>. 187. 



