POLYBIUS 
Antenn# extern# setace® articulis duobus primis majoribus, in oculorum cantho interno 
insert®. 
Pedipalporum geminorum externorum caulis interni articulus secundus ad latus internum prope 
apicem emarginatus pro insertione palpi triarticulati, elongato-subconici. 
Pedum par anticum majus aequale didactylum, manibus externe elevato-lineatis : paria 2, 3, 4, 
et 5 (pari 5 praesertim) compressa foleacea natatoria. 
Abdomen maris 5-articulatum segmento antepenultimo longiore basi utrinque abrupte producto: 
FtEMiNAL 7-articulatum ; articulo ultimo praecedente abrupte angustiore. 
Test# margo anticus arcuatus, semicircularis, lateribus 5-dentatis, sensim postice in angulum 
convergentibus, apice subtruncato : diametro transverse submajore : orbita postice externe 
bifissa, subtus externe unifissa, angulo interno imperfecto. 
Oculi pedunculo suo brevi crassiores. 
External antennae setaceous, with the two first joints largest, inserted into the internal 
canthus of the eyes. External double pedipalpes, with the second joint of their internal 
footstalk notched near its apex, for the insertion of the palpi, which are three jointed and elon- 
gate-conic. Anterior pair of legs equal, didactyle, the hands externally with elevated lines ; the 
other pairs, especially the last, compressed and formed for swimming. Abdomen of the male 
five-jointed; the last joint but one longest; its base on each side abruptly produced. That of the 
female seven-jointed ; the last joint abruptly narrower than the one before it. Anterior margin 
of the shell, semicircularly bent, its sides with five teeth, gradually converging into an angle 
behind, where it is truncated: its transverse, exceeding the longitudinal diameter : orbit behind 
externally with two fissures, beneath externally with one ; its internal angle imperfect. Pedun- 
cle of the eyes narrower than the eyes themselves. 
The only species of this genus hitherto discovered, is described below. 
POLYBIUS HENSLOWII. 
Tab. IX. — b. 
P. testa planiuscula moderatim convexiuscula obscurissime granulata utrinque 5-dentata : 
dentibus brevibus latis, fronte trilobo : lobo medio angustiore. 
Fig. 1. Polybius Henslowii mas. 2. femina. 3. maris abdomen. 4. feminae abdomen. 
This species was first communicated to me by John Henslow, Esq. who found it in the net 
of a Herring fisher, on the Northern coast of Devon, in 1817. It was taken under similar 
circumstances in Pilchard-nets, off Bigbury Bay, in the South-Western coast of Devon during 
thesame season by C. Prideaux, Esq. I have since received it from the Rev. Dr. Goodall, Provost 
of Eton, by whom it was observed in considerable plenty on the shore of Dorset opposite 
Portland Island, amongst the refuse from the nets of Fishermen. 
Since writing the above, I have observed in the collection of the Linnean Society, a spe- 
cimen of this species, which w’as taken off the coast of Spain, by the Rt. Honorable Sir Joseph 
Banks. 
