METAZOA COELENTERA. 135 



horizontally by walls (fig. 5, summit view; fig. 6, vertical 

 section). The moniliform rays may be seen in fig. 5, in 

 the ridges between the rows of four-walled cells. 



The specimens described by Whitfield (figs. 4-6) 

 showed no upper valve ; in fact, there was nothing to 

 indicate a molluscan character in the genus, such as is 

 plainly seen among the Rudistae. At the same time 

 the genus is different from any of the operculated corals, 

 although it is placed in this group provisionally until more 

 perfect specimens can be obtained. 



The single form Zaphrentis (No. 214) of the family 

 Zaphrentidae has a bilateral arrangement of the septa. 

 The "pit" or fossula usually contains a shorter septum. 

 Here were probably the mesenteries that bore the repro- 

 ductive organs. The septa are contorted at the center 

 and the tabulae are not clearly defined, while there is 

 scarcely any vesicular structure. 



Cyathaxonia prolifera McChes. (No. 215), is a single 

 form with septa arranged radially and a central projecting 

 columella. The young Cyathaxonia has an epitheca on 

 the end, which is very delicate, so that it is usually worn 

 off and is seldom seen in fossils. 



Heliophyllum hallilL. & H. (No. 216), is an illustration 

 of a single Cyathophylloid coral. It has the form of a 

 flaring shallow cup. The epitheca is seen on the outside, 

 while the vertical septa are distinctly seen within the cup 

 and are radially arranged. Between the septa on the 

 outer side there is more or less vesicular structure ; the 

 tabulae cannot be made out in the specimens but the ridges 

 on the septa are plainly seen and appear like cross bars 

 between the septa. 



Acervularia ananas Linn. (No. 217), is a colonial form 

 consisting of many coral animals that lived closely to- 

 gether. Here there is an external epitheca. The septa 

 extended to the central bag, and below this organ to the 

 center. They are indicated on the surface of the coral 

 by radiating lines. The vesicular structure has largely 



