* 
Geographical Distribution of Crustacea. 15 - 
Among the Amphipoda, out of fifty genera of Gammaridea, 
only seventeen are known to contain tropical species; nine are 
exclusively tropical, and but ten, including these nine, have 
more tropical than extra-tropical species. 'l'he Caprellidea and 
Hyperidea embrace thirty genera, fifteen or.sixteen of which 
include tropical species. 
''he variety of extra-tropical forms compared with the tropical, 
is hence very great. 
HL. From the tables, the ratio of extra-tropical and tropical 
species in the | 
Isopoda, is ! É ; : P t t 451 
Anisopoda, : : 3 . a pid 
Amphipoda, . : ; . 3 2d 
Among the Isopoda, the Lies are the most decidedly cold- 
water species, and the Cymothoidea, the least so. "The ratio of 
species for the 
Idotseidea;is . ; ; : : ; Sus 
Oniscoidea, 1 . : ; i dog 
Cy mothoidea, : : , d Web 
'T wo-ninths of the tta fbo ddl üdpiedi dea (or nine species) 
belong to the F'rigid zone, and nearly one-tenth of the extra-trop- 
ical Oniscoidea (or nine species) ; while less than a twenty-fifth 
of the Cymothoidea occur in the Frigid zone, and but one of 
these has not also been found in lower latitudes. 
Of the Amphipoda, the Gammaridea are most strongly extra- 
tropical, the proportion being for the extra-tropical aud tropical 
species 31:1; while the ratio in the Caprellidea, is 3:1; and 
in the Hyperidea, 11:1. Out of one hundred and seventy-eight 
extra-tropical species of Gammaridea, sixty-six are Frigid zone 
species, besides two which have been found both in the F'rigid 
and 'lTemperate zones. 
IV. 'l'he genera which extend into the frigid region are the 
following. 'lhe names of those more especially frigid, according 
to present knowledge, are italicised ; and the proportion of .frigid 
species to the whole number of extra-tropical, is mentioned in 
decimals, where they are not exclusively frigid. 
InoripEA.—Idotza (0:3), Glyptonotus. 
OxiscoipEA.—Jz;ra (0:25), Jeridina, Asellus os 20), fuus (0:5), id dd 
Munna (0:66). 
OvworHorpEA.—Ega (0*4). 
SrRoLIDEA.—Serolis (0:2), Praniza (18) Anceus (0:25). 
ARCTURIDEA-— Arcturus (0:5). 
TaNarDEA.—Tanais (0:5), Lériope, Crossurus, Phryxzus, Dajus. 
CaPRELLIDEA.— Proto (0:5), Caprella (0:24), Zgina, Cercops, Podalirius. 
GawMaRIDRA.— ]Dulichia, Siphonccetes, Unciola (05), Podocerus, (0'5), Laphys- 
tius, Orchestia (0:07), Btegocephalus, Opis (0666), Uristes, Anonyz, (0: 9), Leucothoe 
(0:66), .Acanthonotus, (015), Iphimedia (0:6), (Edicerus (05), Gammarus (0:33), 
Melita (0:5), Pardalisca, Ischyrocerus, Michrocheles, Pontoporeia, Ampelisca, Pro- 
tomedeia, Phozus. 
HyPERIDEA.— Hy peria (0:14), Metocus, Tawria, Themisto, (3*0). 
