Geographical Distribution of Crustacea. 9 
the warmer seas afford only small species half an inch in length ; 
there is a Pterelas over an inch in length, while the Egide o 
the tropics 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. ‘I'he species of Serolis are an inch to two 
inches long. Thus, through the Idoteide, the Hgide, Serolide, 
Spheromide, Caprellidea, and Gammaridea, the largest species 
belong to the colder seas, and the giants among Tetradecapods, 
are actually found in the Frigid zone. 
Among the Hyperidea there is one gigantic species, belonging 
to the genus Cystisoma, which is over three inches long. It 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 Turia, was from the Frigid zone. 
II. Again, the Tetradecapoda of extra-tropical waters are 
the highest in rank. Among the Isopoda (which stand first), the 
Idotezidea 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 Serolide, the highest of 
the Anisopoda, are cold-water species. e Orchestie among 
the Amphipoda, although reaching through both the Torrid and 
Temperate zones, are largest and much the most numerous in 
the latter. 
are usually very smooth and often polished species. There are 
the spinous boreal Crangons, the species of which genus in the 
Dulichia are spinous genera. e | 
third pair of caudal stylets in some cold-water Gammari, which 
have the branches spinulous instead of furnished with a few mi- 
Palinuride and species*of Stenopus. Such facts, however, do 
‘ot lead to any modification of the previous remark; for the 
tendency observed is still a fact as regards the several genera men- 
tioned ; moreover the spinous tropical species are few in number. 
_ Stoonp Szems, Vol, XIX, No. 55.—Jan., 1855. 2 
