828 REPORT—1896. 
Discina) even generically identical. The demand for time to originate the group 
is quite as grasping as that of the others we have been considering. 
All the classes of Echinoderma, except the Holothurians, which do not possess 
a structure favourable for fossilisation, are found early in the Paleozoic rocks, 
and many of them inthe Cambrian. Although these early forms are very different 
from those which succeeded them in the later geological periods, they do not possess 
a structure which can be recognised as in any way primitive or ancestral. The 
Echiaoderma are the most distinct and separate of all the Ccelomate Phyla, 
and they were apparently equally distinct and separate at the beginning of the 
fossiliferous series. 
In concluding this imperfect attempt to deal with a very vast subject in a very 
short time, I will remind you that we were led to conclude that the evolution of 
the ancestor of each of the higher animal Phyla probably occupied a very long 
period, perhaps as long as that required for the evolution which subsequently 
occurred within the Phylum. But the consideration of the higher Phyla 
which occur fossil, except the Vertebrata, leads to the irresistible conclusion that 
the whole period in which the fossiliferous rocks were laid down must be 
multiplied several times for this later history alone. The pericd thus obtained 
requires to be again increased, and perhaps doubled, for the earlier history. 
In the preparation of the latter part of this address I have largely consulted 
Zittel’s great work. I wish also to express my thanks to my friend Professor 
Lankester, whom I have consulted on many of the details, as wellas the general plan 
which has been adopted. 
The following Papers and Reports were read :-— 
1. On the Cultivation of Oysters as Practised by the Romans. 
By R. T, Gonrner, JA. 
9. On the Function of certain Diagnostic Characters of Decapod Crustacea. 
By Waurer Garstane, I/.A., Fellow of Lincoln College, Oxford. 
The author deals with the functions of various minor characteristics of Decapod 
Crustacea, especially the Brachyura. 
A crab’s carapace shows two regions subject to great variability of form. 
These regions are— 
1. The frontal area between the orbits. 
2. The pair of lateral margins. 
The variability consists in the absence or presence of spines and teeth, and the 
varying length, shape, and number of these structures. These characters are 
employed by systematic writers to distinguish the different species and genera 
from one another. 
The author's investigations show that it is not merely the function of the 
spines and teeth which is to be considered, but also the function of the spaces and 
notches between them. 
The frontal area of crabs is frequently either 3- or 5-toothed—z.ec., either 
9- or 4-notched. Examination of living crabs shows that the notches are corre- 
lated functionally with the play of the two pairs of antenne. When the frontal 
area is 3-toothed (e.¢., Portunus pusillus) the first antenne are lodged in the two 
notches, and the second antennz project on each side of the frontal prominence. 
When the frontal area is 5-toothed (e.g., Polybius Henslowit) the first antennze 
are lodged in the inner, and the second antennz in the outer pair of notches. 
This type of denticulation is simply an arrangement by which crabs may have 
their antennz protected by a projection of the frontal area, while the possibility 
of free movement for the antenne is provided by the notches along its margin. 
It is scarcely needful to point out that the antenne of a crab are organs of great 
importance to it in the search for food, and that in the case of the antennules a 
