16 Geographical Distribution of Crustacea. 
The Spheromide are nearly all cold-watei species, though 
not reaching into the Frigid zone. "lhere are forty-nine known 
species of Spheromidz in the "T'emperate zone, and but four in 
the 'l'orrid. —/Seroiis is a peculiar cold-water form, belonging 
mainly to the subfrigid and frieid regions. X Orchestia is to a 
large extent of the 'l'emperate zone, while A/lorchestes is more 
equally distributed through the torrid and temperate. Amphi- 
thoe, as restricted by us, is alike common in the torrid and tem- 
perate regions ; while Iphimedia, the other section of the old 
group, is "mainly a cold-water genus. : A 
The Hyperidea are mostly tropical genera. 
V. 'The species and genera of 'letradecapoda are not only 
most abundant in the extra-tropical regions, but besides, the indi- 
viduals of species appear to be more numerous, or at least not. 
less so. At Fuegia, the quantity of Gammaride collected on 
bait dropped in the water was exceedingly large ; and in no re-. 
gion visited by us, did we find evidence of as great profusion. 
The Spheromae were also very abundant along the shores. 
VI. Moreover, the species of extra-tropical waters are the 
largest of the tribe. In the Frigid zone, there are Idotaide 
three to four inches long, while the average size of the tropical 
species is less than three-fourths of an inch; there are Sphe- - 
roms an inch long, while those of the tropics seldom exceed a 
fourth of an inch ; there is a Lysianassa three inches long, while 
the warmer seas afford only small species half an inch in length ; 
' there is a Pterelas over an inch in length, while the ZEgidze of 
the tropies are less than half an inch. "The Gammari of the: 
tropics are small slender species, not half the size of those of 
the colder seas.  'l'he species of Serolis are an inch. to two 
inches long. 'l'hus, through the Idoteide, the ZEgide, Serolidz, 
Spheromidea, Caprellidea, and Gammaridea, the largest species 
belong to the colder seas, and the giants among "T'etradecapods, 
are actually found in the F'rigid zone. | 
Among the Hyperidea there is one gigantic species, belonging 
to the genus Cystisoma, which is over three inches long. 1t is 
reported from the Indian Ocean, but whether tropical or not, is 
unascertained. Of the species 'of this group examined by the 
writer, the largest, a 'Tauria, was from the Frigid zone. 
VIL. Again, the "T'etradecapoda of extra-tropical waters are. 
the highest in rank. Among the Isopoda (which stand first), the 
Idotceidea appear to be of superior grade, and these, as observed, 
are especially developed in the colder seas, reaching their maxi- 
mum size in the Frigid zone. Again, the Serolidce, the highest of 
the Anisopoda, are cold-water species. "The Orchestize among 
the Amphipoda, although reaching through both the 'T'orrid and 
'emperate zones, are largest and much the most numerous in 
the latter. 
