METAZOA COELENTERA. 137 



cubensis^ M.-Ed. & H.) (PL 224), is one of the more 

 generalized members of the family. It is disc-shaped 

 (PL 224, fig. i) like the original basal plate of the 

 Madreporian skeleton. Antillia offers an illustration of 

 the co-existence of the epitheca and theca in one zoon. 

 The epitheca, which is well developed in this species, is 

 shown in fig. 2, and also the central small area of attach- 

 ment. 



Cladocora caespitosa Lam. is seen in the glass model 

 (No. 225). At the left is a single zoon much enlarged,, 

 and just back of it is the colony. The theca is present 

 and the ridges on the outside correspond to the septa. 

 Vesicular structure exists though in small quantities, and 

 the epitheca is only slightly developed. 



The little Astrangia danae Ag. (No. 226 ; No. 227,, 

 skeletons attached to a stone), is the only coral living in 

 our New England waters. It is a colonial form and the 

 corallites are connected by the coenenchyma. The septa 

 unite at the center in a columella and there is no epitheca. 



There are many corals, like Mussa, Manicina, and the 

 like, that increase by a process of incomplete fission which 

 results in winding furrows with such indistinct thecae 

 that often the limits of the different skeletons cannot be 

 made out with certainty. 



The septa in Mussa tenuidentata M.-Ed. & H. (No. 

 228), are large and toothed and the columella is spongy. 

 In some specimens the epitheca is slightly developed and 

 in others it does not exist. According to Martin Duncan * 

 the young of this genus cannot be distinguished from 

 simple Astraeidae of the Antillia type. Mussa increases 

 by fission, as we have said, and the process is often 

 illustrated in one specimen where the original circular 

 corallite may be found, and also more advanced corallites 

 that are elongated, constricted, and nearly or wholly 

 divided. 



1 Quart. Journ. Geol. Soc. London, LI, 1895, p. 259. 

 2 Journ. Linn. Soc. London, Zool., XVIII, 1884, p. 83. 



