312 _ M. T. C. Winkler on 
the carapace. They differ only, as we have seen above, 
in the presence of a movable scale in the Glyphee and the 
deficiency of that organ in Areosternus. On the other hand, 
the basal joint of the outer antenne of the latter is armed 
at the outer angle with a small spine. Is this spine a rudi- 
mentary protective lamina ? 
The legs of the first pair in the Glyphee are much more 
robust than those of the succeeding pairs ; they do not possess 
pincers, but are monodactyle. We may say precisely the 
same thing of the anterior legs of Arwosternus. On com- 
paring an anterior limb of Glyphea tenuis, Opp., with a leg 
of the first pair of Arwosternus, one is struck with the 
incontestable resemblance which exists between these two 
organs. We recognize in these limbs the same structure, the 
same form of joints, the same three or four conical spines at 
- the inferior margin of the propodite, and especially the same 
single small triangular finely pointed finger. 
M. De Man says of the other ambulatory legs of his Ar«o- 
sternus that they gradually become shorter and are formed 
like those of the Palinurt. One cannot judge otherwise of 
the last four pairs of ambulatory legs of the Glypheew ; the 
analogy is here incontestable. 
Arceosternus is furnished with natatory false legs; they are 
of an ovoid pointed form and of foliaceous structure. I have 
observed a similar natatory leg in one of the specimens of 
Glyphea pseudoscyllarus in the Musée Teyler, as already 
stated. On comparing the enlarged figure of this organ 
with the false feet of Arwosternus, one is struck with the 
great resemblance of these parts. . 
From the enumeration of this multitude of analogies, com- 
' pared with the very restricted number of differences between 
the fossil Glyphee and the existing Arcosternus, it is easy to 
conceive the idea that the genus Areosternus is derived from 
the genus Glyphea, that the same form of crustacean which 
already existed at the Triassic epoch, has maintained itself, 
with some modifications, during all the geological periods 
which have succeeded the Trias to the present day. I there- 
fore see in the Ar@osternus Wienecket, De Man, the last 
representative of the G'lyphee, a genus of Crustacea which in 
its turn was a descendant of the genus Pemphix. 
VIII. Considerations and Observations. 
In the preceding I believe I have demonstrated the con- 
tinuation or uninterrupted succession of a special form of 
Crustacean from the Trias to the present time—a form which 
presented itself first as Pemphix, afterwards became modified 
