8 Geographical Distribution of Crustacea. 
species 34:1; while the ratio in the Caprellidea, is 3:1; and 
in the Hyperidea, 13:1. 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 Frigid 
and Temperate zones. 
The genera which extend into the frigid region are the 
following. The 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. 
Inotzipea.—Idotea (0° 3), Glyptonotus. 
Ontscoinra—Jaera (0°25), Jeridina, Asellus (0-20), Janira (0°5), Henopomus, 
Munna (0°66). 
YMOTHOIDEA.— Alga (0°4). 
Srrormpea.—Serolis - 2), Praniza (0°15), Anceus (0°25). 
Axcrurmea—Arcturus (0°5). 
TaNatpea.—Tanais (0° 5), Liriope, Crossurus, Phryzus, Dajus. 
CaPreLtmpEa.—Proto (0°5), pois (0°24), gina, Cercops, P 
MariDEa.— Dulichia, Siphonecetes, Unciola (0°5), Polncea, Ob 8), Laphys- 
- tius, Orchestia (0-07), Btgeephal, “Opis (0 66), ee Anonyz, (0° 9), Leucothoe 
(066), Acanthonotus, (0°75), Iphimedia (0), CEdicerus (0°5), Gammarus (0°38), 
— wage (0° a3 Pardalisea etme Michrocheles, Pontoporeia, Ampelisca, Pro- 
jibe state (014), Metecus, Tauria, Themisto, (3°0). 
The Spheromide are nearly all cold-water species, though 
not reaching into the Frigid zone. There are forty-nine known 
species of Spheromide in the Temperate zone, and but four in 
_ the Torrid. Serolis is a peculiar cold-water form, belonging 
mainly to the subfrigid and frigid regions. Orchestia is to a 
gronP) is giro a cold-water genus. 
e Hyperidea are mostly bigel ag genera. 
The species and genera of Tetradecapoda are not only 
most abundant in the presi regions, but besides, the indi- 
os visited by us, did we find evidence of as great profusion. 
Spherome were also very abundant along the shores. ~ 
Joreover, the species of extra-tropical waters are the 
“the tribe. In the oh id zone, there are Idoteide 
ches long, while the average size of the tropical 
three-four hap inch ; ‘there are ‘Sphe- 
Sie elon 
