316 On Pemphix, Glyphea, and Areosternus. 
force of resistance, a tenacity which nothing could overcome. 
Although this form has certainly undergone some modifica- 
tions (of which we shall speak presently), in general it has 
remained the same as it was during this long series of ages ; 
it has not been able to change its monodactyle feet into 
pincers ; it has not been able to conceal its long tail beneath its 
carapace. It is supposed that it is a progress in organization 
if the monodactyle foot becomes changed into a didactyle 
pincer; it is believed that in these pincers the didactyle 
Crustacean possesses a more effective means of seizing its 
prey than the monodactyle Crustacean has in its claws. It 
is also supposed that it 1s an advance in the organization of 
the Crustacean when the abdomen bends so as to remain con- 
cealed beneath the carapace ; it is generally believed that the 
Brachyurous Decapod Crustacean is the highest type of the 
organization of the Crustacea. And yet the generic form of 
the Glyphee has survived through geological ages; it has 
been victorious in the battle of life, 1 in which its contempo- 
raries, Eryma, Megachirus, Hryon, and several other genera, 
have succumbed*. 
The surface of the body of the Glyphew has not remained 
without alteration during the many ages of their existence ; 
there is a considerable difference between the first representa- 
tive, Pemphix, and the last, Arwosternus. But these changes 
of external characters do not merit the name of essential; they 
are only unimportant modifications with reference to the vital 
functions. In the first place, the tubercles, which are so 
highly developed in Pemphix, appear much less robust, and 
especially less numerous, in the carapace of the Jurassic 
Glyphee : there are even some from the Kellowian, and 
especially a species from the Cretaceous, of which the carapace 
is nearly smooth ; while the carapace of the last representative, 
Arecosternus, is adorned only with small and but slightly 
elevated plates, the almost imperceptible remains of the great 
tubercles of its Triassic ancestor, Pemphix. 
The Glyphee are not the only animals the existing repre- 
sentatives of which no longer present the ornamentation of 
the outer integuments of their ancestors. The fishes of our 
present waters do not possess the scales adorned with tuber- 
cles, hollow dots, beaded strie, &c. of the Gyrodontes, the 
Belonostom?, the Catwr’, &c. which lived in Jurassic waters. 
We are certainly justified in seeing in the slight elevations, 
the squamiform rugosities of the carapace of Ar@osternus, 
* The author here enters into a long digression upon the question 
whether the acquisition of additional parts constitutes an advance of 
organization, which we have not thought it desirable to reproduce. 
