Pemphix, Glyphea, and Areosternus. _ 315 
of species of Glyphea still further increases ; we find here G. 
neocomiensis, Rob.-Desv., G. cretacea, M‘Coy, G. Cartert, 
Bell, G. Lundgreni, Schliit., and an undetermined species, 
Glyphea, sp., Dixon. In the Tertiary the genus diminishes 
in number of species; there are only three—G. numismalis, 
Opp., G. Hauensteint, Mey., and the species placed among the 
Palinurt by Desmarest. Finally, in the Quaternary or actual 
period the number of species decreases considerably ; we know 
only a single species, Areosternus Wienecket, De Man. 
The following graphic Table enables us to follow the alter- 
nate progressive and retrograde course of the genus Glyphea 
through the geological ages of the globe. 
Graphic Table of the Genus Glyphea. 
| \ | 
| 3s | | 3 fan | 
| ~ | fi seaiees 24 & | | | sid 
ee Bee cee ges Onl as . (a s So a | = | 
er} a #5] = © = q |e 6 T=} s eres | 
a S| ae) eet | NE ep shea Sst is) Meee alee 
on ro) I = iS 25 4 D 3S oO (<b) i = 
e2o _ a = & = (eo) 4 20 & o g 3 3 @ 
AP Si(ElS(SiSl/SlS SSlElalelElR 
=) Oa fo) ort ot b=) Oo ie I 3S 4 ian Oo = 
bol 
Alben bes es a eS) Sp hora lS TM bl outea oe 
SPENSER ae i ces z apes r. i ees SESS cane ae} 
| 
| 
This ‘Table teaches us that the genus Glyphea has existed 
during the innumerable ages which have succeeded one another 
from the Triassic epoch to the present time, that it first ap- 
peared in the form which has been named Pemphiz, that it 
traversed the Jurassic, Cretaceous, and Tertiary periods, and 
that it seems now to be approaching extinction in the form to 
which the name of Arosternus has been given. An exis- 
tence so long and uninterrupted shows us that this form of 
Crustacean has had a very considerable vitality, a remarkable 
21* 
