CRUSTACEA. 
119 
Fam. Thelphusiadoe. 
Genus Potamia, (Latr.) (Boscia, Edwards.) 
Of two closely allied species of this genus, pre- 
served without labels in the collection of the Aca- 
demy, the only very distinct character that can be 
made use of for determining, which is the P. dentata 
of Latreille, is this, viz., that the orbits are entire ; 
one of the present species agreeing with the de- 
scription in this respect, and not essentially differ- 
ing from it in other points, as far as can. at present 
be determined, I have supposed, therefore, to be the 
P. dentata. 
P. dentata, (Latr.) Mus. Acad. 
Testa depressa, utrinque oblique impressa; fronte angus- 
tata, bilobata, truncata. 
Front between five and six-twentieths of the 
width of the carapax in its greatest diameter, not 
bifid, but divided by a superficial groove into two 
truncate lobes; on each side of this groove is a 
small transverse indentation ; orbits without a notch 
at the outer angle ; a very profound and oblique 
groove, extending from the antero-lateral margin of 
the carapax toward the median impression, in a 
direction to form with it an obtuse angle, but in- 
terrupted a little above the middle ; hands unequal 
in the male, index curving downward ; many ex- 
tremely minute teeth border the lateral margin of 
the carapax, and the upper edge of the feet ; under 
