ADULT COLONY. 41 



of the madreporarian skeleton, following along lines initiated by Pratz (Palse- 

 ontographica, vol. xxix). Mr. T. Wayland Vaughan has given a resume 

 of the subject in the introduction to his paper on The Bocene and Lower 

 Oligocene Coral Faunas of the United States (1900). 



When the larger septa of Siderastrea are examined sideways, under a 

 low magnification, they present the appearance of the three septa shown on 

 plate 10, fig. 63. The peripheral vertical boundary of each septum consists 

 of a narrow, continuous, nearly straight ridge, which is the broken surface 

 of the thecal wall, really a part of the adjacent septum. Next this is the 

 synapticular area, the synapticula being arranged rather closely in several 

 vertical rows. The surface as a whole is striate, becoming distinctly ridged 

 and grooved as the margin is approached. The septum terminates centrally 

 and above in a strongly serrated margin, the teeth being almost conical in 

 shape, continuous with the ridges, and varying but little in size. Minute 

 granules, usually terminating in one or more sharp points, occur over the 

 whole surface, including the synapticular area and even the marginal spines. 



On septa of the second and third orders may also be seen a vertical row 

 of synapticulum-like structures near their inner border. They are shown on 

 the right (central) margin of the left septum on plate 10, fig. 63, and represent 

 the line of fusion or coalescence of the next adjacent septum in the series 

 the third with the second, and the fourth with the third. They do not occur 

 on septa of the first order, as none of the other septa fuse with these (cf. plate 

 10, fig. 64). The disconnected character of the bodies serves to demonstrate 

 that the central union of one septum with another by the internal margin is 

 not continuous, but interrupted in character. It is best regarded as taking 

 place along the spinous or toothed edge of the smaller septum, in the same 

 way as the complete septa of the first and second orders fuse in an interrupted 

 manner with the columella by their spinous margins. In Siderastrea Miss 

 Ogilvie (1897, p. 179) regards the direct lateral coalescence of the septal 

 surfaces belonging to different septal cycles as homologous with 'the synap- 

 ticular union of septa, but it may be pointed out that the fusion is altogether 

 on the part of one of the septa, not a simultaneous growth from two adjacent 

 septa, as in synapticula proper. The interrupted coalescence of the septa, 

 both with one another and with the columella, necessarily leads to the pro- 

 duction of foramina near their inner edge, some of which are shown to the 

 left in plate 10, fig. 63. 



The septal striae are directed upward and inward in a half fan-shaped 

 manner, starting from the vertical thecal wall. Those on adjacent septa 

 belonging to contiguous calices radiate in an opposite manner, each towards 



