RUGOSA. 



209 



is known as the " fossula " or " f ossette " . (fig. 98, B, and 

 fig. 99). This space appears to take the place of one of the 

 four principal septa, and usually presents itself as a more or 



Fig. dd.Zaphrentis cornicula, the walls of 

 the ealice broken away, and showing the " fos- 

 sula," of the natural size. Devonian, America. 

 (Original.) 



Fig. 100. A, A few calices of Stau- 

 ria astrceiformis, enlarged Silurian ; 

 B, Anisophyllum Agassizi, slightly 

 enlarged ; c, Calice of same, viewed 

 from above DevonUfi. (After Milne- 

 Edwards and Haime.) 



less conspicuous depression or groove in the ealice. Some- 

 times there may be two small lateral fossulse, and in other 

 cases (Omphyma) there are four shallow fossulas arranged in 

 a crucial manner. In the third place, the corallum of the 

 lluyosa generally exhibits tabulse in conjunction with well- 

 developed septa ; whereas in the Zoantharia sclerodermata, 

 if the tabulse are conspicuously developed, the septa are 

 rudimentary or wanting, and vice versa. The tabulae of the 

 Ruyosa may be " complete," passing completely across the 

 visceral chamber from side to side (fig. 98, c), or they may 

 be confined to a larger or smaller central area. Lastly, the 

 VOL. I. O 



