DKCAI'ODA. 



185 



ACILEUS, Leach. 



Six segments in the tail, but the four posterior tarsi are arcuated 

 or falciform ; the ocular pedicles are always salient and present a 

 tubercle ant.-riorly *. 



Next conic 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 antennae is separated by a considerable 

 space from the superior margin of the buccal cavity. The ocular 

 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. 



LKPTOPODIA, Leach. 



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 

 (lentated point J. 



The latter Trigona differ from the preceding in the dissimilitude of 

 their interior 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 the last joint a forceps or 

 didactyle hand. The form of the shell is that of the Leptopodise, and 

 the tail presents the same number of segments : but the feet are 

 much 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 progressively 

 to increase from the second to the fourth, but the two last are very 

 small, licnt. but ^lightly visible, beardless, and apparently useless. 

 Tin- tail is membranous with three crustaceous and transverse spaces 

 on the sides, and another on the end, representing the segmcntary 

 divisions. The eyes are approximated inferiorly. The external 

 foot-jaws are elongated and salient, and the shell is triangular, ex- 



7, 8; Inachus Ifptoriitchits, ejusd., Ib., x.\ '.rtribulus, L. ? Near 



the luachi comes a new genus lately established by M. Guerin, called Eurypode, 

 minutely described nnd can-fully figured, Mem. du Mus. ;. XVI. It ap- 



proaches that of Inachus, but the ocular pedicles arc always salieut; the post-abdo- 

 men is composed of seven completely separate segments in both sexes, and the 

 penultimate joiat of the feet, or the metarsus, is inferiorly dilated and compressed. 



* Acfufttf Crmchii, Leach, Malac. Brit., x\ 



f Macropodia tenuirostri*, Leach, Malac. Brit., xxiii, 15? Inachus longirostrii t 

 Fab. ; .l/./m./j. /./i,i/i,/ M | HI , Lcnch, Ib., xxiii, 6. 



I Inachus sagittariiu, Fab. ; Leach, Zool. Misc., Ixvii. 



Factors Bosdi, Lench, Zool. Misc., Ixviii. 



