INTRODUCTION. 
The second division of the Actinozoa, represented in the cretaceous deposits of 
the Trichinopoly district in Southern India, comprises the corals, — Anthozoa, or 
Polypi, as they are often called in zoological manuals. They have yielded 57 
species, of ■which the majority occurs in the lowest beds of the scries, the Ootatoor 
group, while the two higher divisions, the Trichinopoly and Arrialoor groups, are 
comparatively poor in corals, — just the reverse of what I formerly stated respecting 
the Gastropoda and Pclecypoda. The number of species which liad already been 
described from European cretaceous deposits is small, but the geological results, in 
point of comparison of our fauna and its age with that of foreign deposits, is rather 
an interesting one, as I shall have occasion to notice at the end of the detailed 
descriptions. 
The smaller the animals arc, the more steadily and energetically tliey appear to 
work, in order that they may replace by numbers what they lose by individual size. 
Indeed, even setting aside the interest Avhich the study of corals possesses for the 
morphologist and the systematic zoologist, few other even of the higher classes of 
tlie animal kingdom can compete with the importance, which the corals possess, 
and for ages past have maintained, in the economy of nature. The distribution of 
the corals in the different depths of the sea has been for years past studied with 
considerable interest; and the recent researches in deep sea dredgings are adding 
largely to the information, which is placed at the disposal of the geologist. Need 
I mention the enormous value which Darwin’s and Dana’s studies of the forma- 
tion, extent, and distribution of coral reefs possess for geological research ! It is, 
I believe, justly asserted that more-than one-half of our ancient limestone forma- 
tions is to be attributed to the existence of corals and their colonies forming reefs. 
What greater help can a surveying geologist find, than is afforded to him by the 
discovery of an ancient coral reef, or of a reef-limestone ! If he had been up to that 
time in doubt about the stratigraphical series of his beds or formatious, he finds 
himself upon that discovery quite at home. He knows where he has to seek for the 
ancient land ; he looks after certain animal forms in the lagoons ; after others in 
and on the coral limestone; and the thickness and character of the cropping out 
of the limestone indicate to him the relation of the beds beyond the reef. 
( 1^11 ) 
