ACH EUS. 
Antenne externe distantes setaceee ante oculos ad rostri latera inserte, articulis duobus basi- 
laribus reliquis distincte crassioribus : secundo primo duplo longiore at tenuiore : articulis 
aliis elongatis. 
Pedipalpi externi cauli interno articulo primo apice interiore valde producto: articulo secundo 
subtriangulato ; angulis rotundatis. 
Pedwm par anticum majus didactylum ; par secundum unguibus rectis ; par tertium unguibus 
gradatim arcuatis ; paria quartum et quintum unguibus abrupte et valde curvatis. 
Testa subtriangularis parce spinosa, antice breviter rostrata : rostro fisso. 
Oculi distantes (pedunculi articulo secundo antice unituberculato) in orbitas haud retractiles. 
Abdomen 6-articulatum tuberculato-subcarinatum. 
External antenne wide apart, setaceous, inserted on the sides of the rostrum before the eyes: 
the two first joints distinctly thicker than the others ; the second joint twice*as long as the first, 
and more slender ; the other joints elongate. The external pedipalpes with interior apex of 
their first joint very much produced ; the second joint somewhat triangular; the angles rounded. 
Anterior pair of legs largest and didactyle ; second pair with straight claws; the third pair 
with gradually curved claws ; the fourth and fifth pairs with the claws abruptly and much curved. 
Shell subtriangular, with few spines, anteriorly terminated by a short fissured rostrum. Eyes 
distant (with the second joint unituberculated in front) not retractile within the orbits. Abdomen 
six-jointed, with a tuberculated keel. 
The situation of Ach@us, of which one species only has hitherto been discovered, is inter- 
mediate between IJnachus and Leptopodia: it is the only known genus of the Brachyura, 
excepting the latter, whose eyes are not retractile. 
ACHAUS CRANCHII. 
Tas, X XITR=-c. 
A. testa medio tuberculis duobus ; ordine 1, 1, et inter oculos lineis duabus elevatis. 
Fig. 1., Achzus Cranchii rem. mag. nat. 2. Pedipalpus externus auctus. 3. Antenna 
exterior aucta. 4. Oculiarticulus secundus amplificatus. 5. Fam abdomen auctum. 
Mr. John Cranch discovered, by dredging off Falmouth, a single specimen of the female of 
this curious species, which from the developement of its abdomen is certainly adult. 
Whether the tubercle in the second joint of the peduncle of the eyes, be a specific character 
only, or common to the whole genus, is extremely uncertain. 
The legs are very hairy. 
