C E. lieecher — Development of a Paleozoic Poriferous Coral. 209 



the diameter of the completed nealogic stage, resulting in the 

 normal ephebolic or mature condition, as represented on Plate XI, 

 figures 1, 2. Nearly all the full grown specimens found agree in 

 this respect. 



A coralhun rarely presents any departure from the normal number 

 of calices. Plate XII, figure I, is an example of a variation in the 

 number of peripheral corallities, for in this specimen, there are 

 eight in the circle, instead of the usual seven. A variation in the 

 opposite direction is shown in another sjiecimen having five well 

 develo[)ed corallites about the parent cell. Old age characters are 

 expressed in two ways : First, the cell walls become thickened 

 around the margin of the epitheca without destroying the S3anmetry 

 of the corallum, as shown in Plate XII, figure 2 ; Second, by the 

 indefinite and unequal development of the peripheral cells, together 

 with the addition of calices budding from the cells forming the 

 primary circle. One specimen, appearing at first sight as an exam- 

 ple of cell division or fission, is shown in Plate XIII, figure 2. It may 

 be explained as resulting from the abnormal growth of the second 

 and adjacent calices, four and eight. , This lateral impulse further 

 resulted in sending off the small, peripheral, tertiary corallites num- 

 bered in the figures 9, 10, 11, 12, and 13. 



It should be understood that this arbitrary expression of normal 

 and abnormal growths applies only to the species P. lenticulare. 

 The same numerical arrangement will not hold good for genera like 

 Favosites, MicheUnia^ Striatopora, etc. Otherwise, it is believed, 

 the general laws of growth here brought out will hold good for 

 these and other related genera. 



Some doubt may exist as to the propriety of referring the speci- 

 mens illustrated on Plate IX, figures 9-11, to P. lenticulare. Unfor- 

 tunately, material of this kind is rare and difficult to obtain. With 

 the exception of the position and direction of the first bud (figure 

 10), all the characters agree, so far as can be observed, with ordinary 

 specimens of P. lenticulare. The second cell of the corallum repre- 

 sented in Plate X, figure 1, curves rapidly backwards, although at 

 first the axis has an anterior direction. Taking this view of the 

 specimen, Plate IX, figure 1 1, it is not difficult to see how the succeed- 

 ing enlargement and curvature of the bud could extend backwards, 

 thus properly limiting the size of the eighth or last of the primary 

 circlet of calices. 



The method of determining the relative age and succession of the 

 corallites can be seen in Plate X, figures 1, 2, and Plate XI, figure 2. 



