236 Prof. J. E. DuerJen on the 



septa, as their tijjs are iisLuilly perfect. On grinding down a 

 coralliim for a short distance six equal septa are disclosed, 

 radially arranged, and separated by comparatively large equal 

 interspaces. On pages 234-235 four figures are given 

 (figs. 9-12) displaying tlie early stages in the septal develop- 

 ment of this species, starting as before with a primary 

 hexamerism. 



In the above and other species, in which the septal con- 

 stitution has been estaljlished by the process of grinding, it 

 may be objected that if earlier stages than tho^e first repre- 

 sented could be obtained four primary septa might t!ien 

 be disclosed, and the other two would be seen to be but later 

 additions to a tetrameral group ; in other words, that the 

 earliest septal stage is not that indicated as such. Were tiiis 

 the case the dorso-lateral pair here regarded as protosepta 

 would be really the first pair of metasepta. Against this 

 reasonable objection it can be aflirraed that in all cases as 

 soon as any of the primary septa are determinable they are 

 already six in number, all fully developed, practically equal 

 in size, and radially disposed at equal distances apart. Two 

 pairs never appear in advance of a third pair. Moreover, 

 there is never any hint of the third pair being inclined at 

 its origin towards the others, after the manner of develop- 

 ment invariably characteristic of the first and later pairs of 

 metasepta. All the sections representing the appearance of 

 the metasepta indicate that the new septa first arise within 

 the wall of the calice. Their free end is then turned towards 

 the older septum dorsal to them, and as they become larger 

 and extend higher they seem gradually to travel, as it were, 

 along the older septum, until tliey nearly reach the middle of 

 the calice. The centripetal end then becomes independent 

 of the adjacent septum, and is either free or united in a 

 columellar mass. Tlius the metasepta are not truly radial 

 until they are fully formed. These stages are presented by 

 all the metasepta and also exosepta in their devolopment, but, 

 as already stated, they are never represented by any of the 

 first six septa. All the studies on the development of the 

 corallum of recent hexameral corals^ conducted by Lacaze- 

 Dutliiers, (Jr. von Koch, and myself, indicate that six equal 

 se))ta are formed simultaneously in a radiate manner, and 

 such would appear to have been the case with the corals of 

 Palaeozoic times. 



Among a large collection of rugose corals lent me for study 

 by the United Slates National Museum, through the 

 assistance of Prof. C. Schuchert, are several specimens 

 labelled Zaphrentis pusiUa, n. sp. These have j)roved to bo 



