CHARACTERISTICS OF THE SEPTA. 201 



cles. ( Figure 2, plate 8. will lie found on minute examination to show this 

 structure.) These layers are drawn as continuous by Billings, not only 

 from septum to septum but also through the center* It is this erroneous 

 conception of them which has caused the genus to be described as having 

 complete tabulae and as made up of superposed and invaginated cell-cups. 



In radial sections through the septa the cut edges of these layers appeal' 

 as delicate parallel lines, sloping gently from the edge of the calyx down- 

 ward toward the center. Intersected at right angles by the supporting 

 growths they present, in typical forms, a Stromatopora-like appearance 

 (figure 5). As the septum approaches the center the layers become more 

 sharply bent, the side faces are brought more closely together, and there is 

 formed a thin but double septum not to be distinguished from those of 

 ordinary corals. 



As a support for these delicate layers there' are abundantly developed 

 upon the upper surface of each, granular or spinulose processes. In 

 certain specimens of C. magnificum vertical plates are formed which may 

 be somewhat curved or warped, presenting a vermiform appearance under 

 the hand lens, and arranged across the septum (figure 3). These may 

 be over a mm in breadth and continuous upward for several mm. actu- 

 ally intersecting the layers. They may start as simple spinules and 

 gradually widen into plates as they ascend. In certain cases they are 

 simply placed in corresponding, or nearly corresponding, position upon 

 the successive layers. These growths have their flat faces shown in figure 

 2, their edges in figure 5, and their cross-sections in figure 3. < >n the 

 side faces of the septa these growths are reduced to rounded granula- 

 tions, and under this form extend inward to the pit (figure 5). They 

 have been observed here to be at times crowded together into rows ex- 

 tending, for short distances, upward and outward. A rather character- 

 istic roughened appearance is thus given to the septa when viewed from 

 the calyx. 



The forms which may be referred to the genus do not offer advantages 

 for the determination of the order of the interpolation of new septa, 

 owing to their general shape and structure. The widening of the septa 

 at the edge of the calyx endeavors to keep pace with the diametral 

 growth of the corallum, thus giving occasion and necessity for the intro- 

 duction of tew new ones. The septa generally start from the base with 

 an irregular spiral twist in which the foundations are early laid for 

 nearly all that will he needed. A young specimen of <". magnificum with 

 a height of 12 mm and a calyx diameter of 2-'! mm has 72 septa, while 

 a mature specimen of the same species. NO mm in diameter, has hut 86. 

 Another specimen in expanding its calyx from 18 to 100 mm and 



* ('.hi. Jour , new series, vol. \ . pi. i, figs a and e, 

 XXXV— Bum ftnoi Stic, \m. Vol, :, 1891. 



