322 
paleontological geology 
under magnification. On the other hand, certain structures arc 
rather clearly indicated on the epipodites that are wholly wanting 
on the exopodites. Most important of these is a line of denser 
substance running some distance within and parallel to the margin 
of both lobes. On close inspection small denticles are observed 
projecting from one side of this inner line. From these and 
other corroborating facts observed it is inferred that both surfaces 
of the epipodites bore two spiniferous carinae which united on the 
smaller lobe. Except at these carinae the walls of the epipodites 
seem to have been exceedingly thin or at least more tenuous than 
those of the exopodites. On account of their isolated and exposed 
position, not being held together like the exopodites by long over¬ 
lapping fringes of setae, and lying between the endopodites and 
outside the exopodites, they were much more liable to be lost.” 
Walcott. 
Extinction of the Tetracoralla. In a paper by Professor Ray¬ 
mond, in a recent issue of the American Journal of Science it is 
suggested that the extinction of the Tetracoralla at the end of 
Paleozoic time was the result of a chilling of oceanic waters by 
the melting of the Permian Ice-sheet. 
In order to consider this idea quantitatively the following as¬ 
sumptions must be made: (1) That the Paleozoic reef-building 
and solitary Tetracaralla had a habit similar to the present reef 
corals as to depth and temperature, the modern reef-builders 
being confined to shallow tropical and sub-tropical waters; (2) 
that the volume of the ocean has remained constant from Permian 
times tOij the present, except as it was altered by glaciation and 
deglaciation; and (3) that the continental areas, including the 
submerged continental shelves, have been relatively constant from 
Permian to Present Time. 
Taking the volume of the oceans as 1,300,000,000 cubic kilo¬ 
meters, according to Murray and Hjort,^ a change of one degree 
centigrade would give off or absorb 1.30 times 10 to the 24th 
power calories, assuming that a cubic centimeter of water weighs 
a gram and the specific heat of water is one calorie.^ Even in these 
days of oceanographic investigation it is difficult to get an average 
1 Depths of the Ocean, p. 210. 
2 Water does not weigh exactly 1 gram per CC at all temperatures from zero to 
100° C, nor is the specific heat exactly one, nor is it constant from zero to 100° C; 
but these approximations are close enough for the calculations in this paper. 
