1522 CRUSTACEA. 



to the Frigid zone, and nearly one-tenth of the extra-tropical Oniscoi- 

 dea (or nine species) ; while less than a twenty-fifth of the Cymothoi- 

 dea 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 and tropical species 

 3i : 1; while the ratio in the Caprellidea, is 3 : 1; and in the Hype- 

 ridea, 14:1. 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. 



IV. The genera which extend into the frigid region are the follow- 

 ing. The names of those more especially frigid, according to present 

 knowledge, are italicized; and the proportion of frigid species to the 

 whole number of extra-tropical, is mentioned in decimals, where they 

 are not exclusively frigid. 



IDOT-SIDEA. Idotsea (0-3), Glyptonotus. 



ONISCOIDEA. Jaera (0-25) Jaeridina, Asellus (0-20), Janira (0-5), Henopomus, 

 Munna (0'66). 



CYMOTHOIDEA. JEga. (0-4). 



SEKOLIDEA. Serolis (0-2), Praniza (0-15), Anceus (0-25). 



ARCTURIDEA. Arcturus (0'5). 



TANAIDEA. Tanais (0-5), Liriope, Crossurus, Phryxus, Dofus. 



CAPRELLIDEA. Proto (0-5), Caprella (0-24), JEgina, Cercops, Podalirius. 



GAMMARIDEA. Dulichia, Siphonceceles, Unciola (0-5), Podocerus (0-5), Laphystius, 

 Orchestia (0-07), Stegocephalus, Opis (0-66), Uristes, Anonyx (0-9), Leucothoe (0-66), 

 Acanthonotus (0-75), Iphimedia (0-6) (Edicerus (0-5), Gammarus (0-33), Melita (0-5), 

 Pardalisca, Ischyrocerus, Michrocheles, Pontoporeia, Ampelisca, Protomedeia, Phoxus. 



HYPERIDEA. Hjperia (0-14), Metcecus, Tauria, Themisto (3-0). 



The Spheromidse are nearly all cold-water species, though not reach- 

 ing into the Frigid zone. There are forty-nine known species of Sphe- 

 romidae 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 large extent of the Temperate zone, 

 while Allorchestes is more equally distributed through the torrid and 

 temperate. Amphithoe, as restricted by us, is alike common in the 

 torrid and temperate regions ; while Iphimedia, the other section of 

 the old group, is mainly a cold-water genus. 



The Hyperidea are mostly tropical genera. 



V. The species and genera of Tetradecapoda are not only most 



