BATTERSB YIA, PALtEOCYCLTJS, AND ASTEROSMILIA. 
647 
It will be very readily observed that the stout wall, the costae, and the absence of 
epitheca render this genus rather exceptional amongst those of the Palaeozoic fauna. 
The irregular septal arrangement of some of the species, and the presence of one septum 
larger than the others in certain forms, are rugose peculiarities ; but the scanty and 
simple dissepimental endotheca is very differential. 
In Heterophyllia mirabilis the endotheca is very sparingly seen, and it exists in the 
form of simple dissepiments very wide apart, which, as in the Astrceidce , close more or 
less the interlocular spaces. They do not close in the whole of the visceral, axial, and 
interlocular cavities in a horizontal plane, and they are not tabulae in the strict accepta- 
tion of the term. In other species the dissepiments are closer, and, although curved, 
simulate tabulae. True vesicular endotheca is rare, but it exists in most of the specimens. 
The columellary lamina^ curved in some species, but straight in others, is probably pro- 
duced by the soldering of the septal ends, and is not really a true lamellar columella. 
In the specimen of Ileterophyllia Sedgwicki, whose calice is preserved, the formation of 
the septal columella can be seen. The costae, so variable in their structure, afford admi- 
rable specific distinctions ; and those of H. mirabilis are totally unlike any others from 
any madreporarian family. The septa, irregular in number in some species, are then 
rather numerous ; but when they are regular in their arrangement they never number 
more than six. 
The species may be distinguished by comparing the specimens with the following 
fCostae few, large, as polygonal ridges. 
1 Septa very irregular in number. 
j Costae 16 in number, narrow with round tubercles. 
[Septa 14 in number. 
f Costae numerous, flexuous, rounded, bifurcate, granular. 
[Septa 19 in number, grouped in 5 series, 
f Costae projecting, sharp, unequal. 
1 Septa 17 in number, in 5 series and 1 large septum. 
J Costae 6 in number, small, rounded, grooved. 
\Septa 6 in number. 
J Costae large, smooth, rounded, projecting, tuberculate. 
[Septa 6 in number. 
J Costae narrow, rounded, tuberculate and spined. 
[Septa 6 in number. 
fCostae 18 in number, distant, flexuous, small, grooved. 
[Septa 18 to 20 in number. 
The genus may be subdivided into a group with numerous septa and a group with six 
septa. 
In the first subdivision the rugose type is faintly, and in the second the hexameral 
Heterojphyllia grandis 
ornata . . . 
granulata . . 
angulata . . 
mCoyi . . 
Lyelli . . . 
mirabilis . . 
Sedgwicki . . 
