48 CRUSTACEA. 



Inachus, Fab., 



The tail is always composed of six segments; all the tarsi are 

 nearly straight, or but slightly arcuated; the ocular pedicles are 

 smooth, susceptible of being concealed within their fossulae, and 

 there is a tooth or spine, at least in the males, at the posterior ex- 

 tremity of the latter cavities. Doctor Leach has considerably re- 

 duced the original extent of this group(l). 



AcHiEus, 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 anteriorly(2). 



Next come those in which the epistoma is longer than it is broad, 

 shaped like an elongated triangle truncated at the apex, and in whicli 

 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(3). 



Leptofodia, 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(4). 



The latter Trigona differ from the preceding in the dissimilitude 

 of their posterior feet. 



(1) Cancer dodecos P L.; Inachus scorpio, Fab. ; — Inachus Dorsettensis, Leach, Ma- 

 lac. Brit., xxii, A; — Inachus phalangium, Fab.; Inachus dorynchus. Leach, lb.,. 

 xxii, 7, 8; — Inachus leptorinchus, ejusd., lb., xxii, B; Cancer tribulus, L. ? Near 

 the Inachi comes a ne\T genus lately established by M. Guerin, called Eurypode, 

 minutely described and carefully figured, Mem. du Mus. d'Hist. Nat. XVL It ap- 

 proaches that of Inachus, but the ocular pedicles are always salient; the post-ab- 

 domen 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. 



(2) Jlchmis Cranchii, Leach, Malac. Brit, xxi, C. 



(3) Macropodia ienuirostris, hesich, Malac. Brit, xxiii, l—5;Inachuslongirostris? 

 Fab. ; — Maa-op. phalangium, Leach, lb., xxiii, 6. 



(4) Inachus Sagittarius, Fab.; Leach, Zool. Misc., Ixvii. 



