154 A REVISION OF THE ASTACIDA. 
been artificially introduced, according to Dr. Radde, into some of the tribu- 
taries of the upper Koor (the Cyrus of the ancients), which flows eastward 
into the Caspian Sea (Kessler). 
NOTE ON THE FOSSIL ASTACIDA. 
Abundant fossil remains of Crustacea nearly allied to the recent Homaride and Asta- 
cide are found in the Jurassic from the Middle Lias to the lithographic slates of Bavaria 
an Wiirtemberg. These ancient Decapods, belonging to the genera Eryma and Pseudas- 
tacus,* agreed with the lobsters and crayfishes of the present day in having the three 
anterior pairs of legs terminated by pincer-like claws (the first. pair large and powerful), 
the abdominal pleura drawn out into prominent lateral plates, and the outer branch of 
the enlarged posterior pair of appendages or swimmerets divided by a transverse suture. 
The carapace was produced into a prominent rostrum, commonly denticulate on the 
margin; the telson showed no trace of a division into two pieces by a transverse suture 
(agreeing in this regard with the telson of the modern Homaride and Parastacine), and 
was more triangular in outline than in the living forms; the large chelie were nearly sym- 
metrical on the two sides of the body, and the shell granulated or tuberculated, as in 
the Astacidee. If we unite the Homarid and the Astacidee in one tribe, the Astacoidea, 
there can be no reasonable doubt that the Jurassic genera Eryma and Pseudastacus would 
be included properly in this tribe. To them we turn in seeking the progenitors of the 
Homaride and Astacide of our seas and rivers. Unfortunately, these fossils have im- 
parted as yet no information concerning certain important structural features which must 
be known before we can determine whether the Astacine type was thus early differen- 
tiated from the Homarine. I refer to the number, structure, and arrangement of the 
gills; the condition of the last thoracic somite, whether free or fixed; and the structure of 
the anterior abdominal appendages. In our ignorance of these structural characters in 
these marine Jurassic fossils I cannot see the slightest ground for Huxley’s conclusion, 
that in the genus Pseudastacus we already see a differentiation of the Astacine from the 
Homarine type represented by Eryma.t Pseudastacus differs from Eryma in having a 
longer rostrum, longer and thicker antennal peduncle and scale, and in the lack of movable 
spines on the penultimate segment of the fourth pair of legs. In P. pustulosus (Miinst.) 
the inner as well as the outer branch of the swimmerets seems to have been divided by a 
transverse suture. Now, in none of these particulars does Pseudastacus, as distinguished 
from Eryma, approach the Astacidie of the present time. Boast has called attention to 
the fact that the transverse part of the “cervical” groove of Pseudastacus is the same as 
the anterior and more deeply impressed groove (marked ¢ in Boas’s figures) on the cara- 
pace of Eryma, and that it is not homologous with the cervical groove of Homarus and. 
Astacus (c of Boas’s figures), but rather with the anterior slightly impressed groove seen 
on the carapace of Nephrops. 
* For an account of these animals, the reader is referred to the beautifully illustrated work of Oppel, 
Palaeontologische Mittheilungen, Stuttgart, 1862. The Astacus Knorrit of Milne Edwards (Hist. Nat. Crust., 
I. 333), figured by Kuorr and by Desmarest, is probably an Eryma. 
+ Huxley, The Crayfish, p. 343. 
+ Studier over Decapodernes Slegtskabsforhold. Vidensk. Selsk. Skr., 6te Rekke, Naturvid. og Math. 
Afd., Bd. I. pp. 74, 176, foot-note 2, 1880. 
