AMPHIPODA. 
223 
assert that they will cut the threads that keep them there, in 
order to precipitate them into the mud, where they may devour 
them at their leisure. They appear to breed during' the whole 
summer, as females carrying their ova are to be met with at 
various periods. Waders and different Fishes prey upon them. 
For these interesting observations we are indebted to M. D’Or- 
bigny, Senior, conservator of the Rochelle Museum and corre- 
sponding member of that of Paris * * * § . 
The second section — Heteropa, Lat. — is composed of those with 
fourteen feet, the last four of which, at least, are unarmed and destined 
for natation only. It comprises two subgenera f. 
Pterygocera, Lair. 
The thorax divided into several segments; four antennae furnished 
with setae or hairs in bunches; all the feet natatory and the last large 
and pinnated | ; cylindrical, articulated appendages to the posterior 
extremity of the body. 
Apseudes, Leach. — Eupheus, Risso. 
The thorax also divided into several segments, but the two anterior 
feet terminated by a didactyle forceps ; the two following ones clavi- 
form, ending in a point and dentated on the edges ; the next six 
slender and unguiculated at the extremity; the last four natatoiy. 
The antennae are simple. The body is narrow, elongated, and has 
two long setaceous appendages at its posterior extremity^. 
The third and last section — Decempedes, Lat. — is composed of 
Amphipoda, which present but six distinct feet. 
Typhis, Risso. 
But two very small antennae, the head large, and eyes not promi- 
nent ; each pair of feet annexed to its peculiar segment, and the four 
anterior terminated by a didactyle forceps. On each side of the 
thorax are two moveable plates, forming a sort of lids or valves. 
* See Encyclop. Method., article Podoci;re. 
-t This and the following section, in the first edition of the Regne Animal, form 
the second of the Isopoda, that of the Phylihrunchiafa. But independently of our 
having discovered mandibular palpi in some of these Crustacea, the form of the 
subcaudal appendages appears to us to approximate them much nearer to the 
Amphipoda than to the Isopoda. We may also observe that these animals, of 
which we have seen but very few, have not yet been well studied. 
J According to the figure of Slabber — Oniscus arenurius, Encyclop. M^'tliod., 
Atl. d’Hist. Nat., CCCXXX, .3, 4, — the number of feet is but eight; reasoning 
from analogy, I presume it to be fourteen ; besides, if the figure be exact, this genus 
would belong to the next section. 
§ Eupheus ligiotdes, Risso, Crust., Ill, 37 ; Desmar., Consid., 285 ; — Apseudes 
talpa, Leach; — Cancer gammarus talpa, Montag., Trans. Lin. Soc., IX, iv, 0; Des- 
mar., Consid. : XLYI, 9. See the Gammarus heteroclilus, Viviani, Phosphor. 
Maris, II, ii, 12. 
N.B. The genus Rhcea, M. Edwards, Ann. des Sc. Nat. XIII. xiii. A, 292, dif- 
fers from the preceding in the superior antenna;, which are stouter, longer, and 
bifid. 
