THREE CRUISES OF THE “BLAKE.” 
18 
Many groups are remarkable for the variety of their forms, so 
that it is almost impossible to apply to them any classification, 
even that regarded as best established. From the study of these 
groups, most interesting morphological and. paleontological re- 
sults have been derived. Some of these are discussed in con- 
nection with the account of the different zodlogical groups. As 
the corals of the West Indies have been carefully studied by 
Pourtalès, we may dwell more at length on the relations of that 
fauna to their precursors in the tertiary period. 
The corals of the European tertiaries are so well known from 
the works of Milne-Edwards, Haime, Reuss, Seguenza, Duncan, 
and others, that we can compare the living West Indian coral 
faune, both littoral and abyssal, with that of the European 
tertiaries. The resemblance is a striking one, and we may 
safely, from analogy, reconstruct the physical conditions which 
existed in the European tertiary seas, and picture to ourselves the 
depth of the water, the purity of the sea, and the intense aera- 
tion of the waters, far from great bodies of fresh water, which 
must have prevailed in those days over areas where either coral 
reefs or a deep-water fauna flourished.’ 
Fewer deep-sea genera are common to the tertiary and living 
faune of the West Indies than to the European tertiary and the 
living West Indian fauna. This may be due to smaller changes 
of level in the latter region than in Europe. Yet if we take into 
account the fact that the numerous West Indian extinct genera 
belong to families of deep-sea corals, we may safely conclude 
that there have really been important changes of level in the 
West Indian area. The presence of European cretaceous fossils 
rence of the recent stalked erinoids in 
such deep water as compared with that of 
the paleeozoie period may be interpreted 
to represent the conditions necessary for 
the maintenance of the type down to the 
1 The similarity in the deep - water 
types and their fossil representatives may 
not: invariably mean existence under iden- 
tical conditions. We have the most sat- 
isfactory evidence that the erinoids of the 
silurian deposits of the State of New 
York flourished in shoal-like areas, and 
that during the jurassic period their oc- 
eurrence on the coral reefs of that time 
showed these ancient crinoids to have 
lived in much shallower waters than their 
recent allies, the Pentaerinus and Rhizo- 
erinus of the West Indies. The occur- 
present day. In the present epoch depth 
represents, as has been suggested by 
Pourtalés, the great pressure to which 
the heavy atmospheres of earlier periods 
subjected the animals of those days, and 
thus perpetuates conditions recalling 
those of the shoal waters of early ages. 
