Pemphix, Glyphea, and Areosternus. “313 
to give origin to the Glyphee, and finally, after having un- 
dergone some further changes, is at present known as Areo- 
sternus. 'The investigation of the existence of this long series 
of animal forms has made known to us a multitude of pecu- 
liarities with regard to the modifications and bodily changes 
undergone, the grade of generic development, &c. of this form 
of Crustacean. 
Paleontological researches have shown that the most an- 
cient Crustacea were Macrurous, that the Anomura made their 
appearance long before the Brachyura, and that the Brachyura 
did not show themselves until a comparatively recent geolo- 
gical period, namely in the Cretaceous. The most ancient 
Macrurous Decapods have been found in the Bunter Sand- 
stone of Soultz-les-bains; these are forms analogous to the 
genera Gebia and Galathea. After the Bunter we find the 
Muschelkalk, which has preserved for us two forms of the 
genus Pemphix. Inthe Jurassic deposits, including the Lias, 
we meet with a great number of genera of Macrurous Deca- 
poda, known at present under the names of Hryon, G'lyphea, 
Eryma, Pterochirus, Megachirus, Palinurina, Cancrinos, and 
many others. In the Cretaceous again we find several Ma- 
crurous genera, side by side with the first Brachyura. In the 
present day the reverse is the case; in the existing fauna we 
count at least three species of Brachyurous Crustacea for one 
Macruran. The most recent paleontological investigations, 
the most complete treatises upon fossil Crustacea, prove that 
the close of the Cretaceous period and the whole of the Ter- 
tiary period are characterized by a predominance of Brachyu- 
rous Crustacea. It would appear, then, that in the Cretaceous 
period Nature prepared for the production of Brachyurous 
species— species which she scatters in the existing period 
with so much prodigality. The result of carcinological re- 
searches with regard to the predominance of certain forms of 
Decapod Crustaceans is, on the one hand, absolute predomi- 
nance of Macrurous and almost complete absence of Brachyu- 
rous Crustacea in the older strata of our globe, and, on the 
other, a very great predominance of Brachyurous Crustacea, 
with continuation of the Macrurous Crustacea, in the more 
modern deposits. 
The investigations of paleontologists have further taught 
us that each of the different formations of the globe contains 
only remains of Crustaceans of a form proper to it, or, to ex- 
press myself more precisely, that no species of Crustacean of 
a given period has lived during another period, while the 
genus has been able to exist during several consecutive geolo- 
gical periods. For example, none of the specdes of Macrurous 
Ann. & Mag. N. Hist. Ser. 5. Vol. x. zi 
