DECAI'ODA. 
185 
AcHiEus, Leach. 
Six segments in the tail, but tlie four posterior tarsi are arcuated 
or falciform; the ocular pedicles are always salient and present a 
tubercle anteriorly ■* * * * § . 
Next come those in which the epistoma is longer than it is broad, 
shaped like an elongated triangle truncated at the apex, and in which 
the origin of the mediate antennee is separated by a considerable 
space from the superior margin of the buccal cavity. The ocidar 
pedicles are always salient when the head is triangular and termi- 
nated in a point more or less bifid or entire. 
Stenorhynchus, Lam. — Macropodia, Leach. 
Six caudal segments in both sexes; anterior extremity of the shell 
bifid f. 
Leptopodia, Leach. 
- Five segments in the tail of the male; one more in that of the fe- 
male. The shell is prolonged anteriorly into a long, entire, and 
dentated point 
The latter Trigona differ from the preceding in the dissimilitude of 
their posterior feet. 
Pactolus, Leach. 
The four or six anterior feet simple, or without forceps. The in- 
ternal extremity of the penultimate joint of the four posterior ones 
is prolonged into a tooth, forming with th.e last joint a forceps or 
didactyle hand. The form of the shell is that of the Leptopodiee, and 
the tail presents the same number of segments : but the feet are 
mueh shorter ; those of the third pair were wanting in the individual 
which served as the type of this section §. 
Lithodes, LaL 
The Lithodes, as to the form of the first eight pairs of feet, re- 
semble the other Trigona; their length, however, seems jirogressively 
to increase from the second to the fourth, but the two last are very 
small, bent, but slightly visible, beardless, and apparently useless. 
The tail is membranous with three crustaceous and transverse spaces 
on the sides, and another on the end, representing the segmentary 
divisions. The eyes are approximated inferiorly. The external 
foot-jaws are elongated and salient, and the shell is triangular, ex- 
xxii, 7, S; — Inachus leptorinclms, ejusd., Ib., xxii, B; Cancer trihulus, L. ? Near 
the luachi comes a new genus lately established by M. Guerin, called Eurypode, 
minutely described and carefully figured, Mem. du Mus. d’His., Nat. XVI. It ap- 
proaches that of Inachus, but the ocular pedicles are always salient; the post-abdo- 
men is composed of seven completely separate segments in both sexes, and the 
penultimate joint of the feet, or the metarsus, is inferiorly dilated and compressed. 
* Achecus Cranchii, Leach, Malae. Brit., xxi, C. 
-f- Macrupodiu tenuirosfris, Leach, Malac. Brit., xxiii, 1 — 5; Inachus Ivnyiroslris? 
Fab.; Macrup. phaJamjuim, Leach, Ib., x.xiii, 6. 
t Inachus Sagittarius, Fab. ; Leach, Zool. Misc., Ixvii. 
§ Pactolus lioscii, Leach, Zool. Misc,, Ixviii. 
