DECAPODA. 
201 
Eryon, Desmar., 
All the leaflets of the caudal fin are narrowed at their extremity 
and terminate in a point; the external one presents no transverse 
suture. The two filaments of the mediate antennm are very short, 
and hardly longer than their peduncle. The sides of the shell ai’e 
deeply cmarginated. 
I’he forceps of the two anterior claws are narrow and elongated. 
This subgenus was established by Desmarest on a fossil species, — 
Eryon Ciivieri, Hist. Nat. des Crust. Foss., X, 4; CVjnsid., XXXIV, 
3, found in a lithographic, calcareous stone from Pappenheim and 
Aichtedt in the margravate of Anspach. 
Astacus, Gronov., Fab. 
Leaflets of the lateral fins at the end of the tail widened and 
rounded at their extremity ; the external one divided transversely by 
a suture, and the posterior extremity of the mediate obtuse, or rounded. 
The two filaments of the mediate antennae are much longer than 
their peduncle. The sides of the shell are entire, or not incised. 
In some, all inliahiting salt water, the last segment of the tail, or 
that which occupies the middle of the terminal fin, presents no trans- 
verse suture. 
Those whose lateral antennae have a large scale on their peduncle, 
whose eyes are very large and reniform, and the forceps of whose 
two anterior claavs are narrow, elongated, prismatic, and equal, 
form the genus Nephrops of Leach, the type of which is the Cancer 
nor^vegicus, L.; de Geer, Insect., VII, XXI; Herbst., XXVI, 3; 
Leach, Malac. Brit., XXVI. The two anterior claws are furnished 
Avith dentated spines and ridges, and the superior surface of tlie tail is 
sculptured. It is found in the seas of the north of Europe, and in the 
Mediterranean. 
Those in which the peduncle of the lateral antennae i)resents no- 
thing but tv/o sliort })rojections in the form of teeth or sj'ines, wliose 
eyes are neither large nor reniform, and whose forceps are more or 
less oval, compose, with the fresh rvatcr species, the genus Astacus, 
properly so called, of the same author. 
Astacus marinus, Fab.; Cancer ganimarus, li. ; Ilerhst., 
XXV ; Penn., Brit. ZooL, V, x, 21 ; (the Common Lobster). The 
point or rostrum of the anterior extremity of the shell has three 
teeth on each side, and another double one at its base. The an- 
terior claws are very large and unequal ; the largest finger of tlie 
forceps is oval, with great molar teeth, the other is elongated, 
and has numerous small ones. Old individuals are sometimes 
more than half a metre in length. Its flesh is liighly esteemed. 
It is found in the European Ocean, in the Mediterranean, an I 
even on the eastern coasts of North America. Its internal 
structure has been carefully studied by hlessrs. Victor Andouin, 
and Milne Edwards. 
In the fresh Avater species, Avhicli otherAvise resemble the preced- 
ing in their antenmje, eyes, and form of the chiAVs, the last segment of 
