Geographical Distribution of Crustacea. 325 
yura, which is evidence of superiority. These Crangonide, thus 
the highest of the Caridea, are almost exclusively cold-water 
pecies. 
In the family Palemonide, some genera have the anterior legs 
furnished with stout hands, while in others the second is the 
stout chelate pair. ‘The former, for the reason just allnded to 
while speaking of the Crangonide, and elsewhere further ex- 
plained, are superior in rank. It is among these genera of this 
superior grade, the Alpheine, that we find the cold-water and 
boreal species. The genus Hippolyte alone contains thirty-seven 
cold-water species, nineteen of which are of the Frigid zone; 
and there are only eight torrid species. 
On the contrary, among the Palemoninze, the inferior group, 
there are forty-six torrid to twenty-two extra-torrid species; and 
only one of the latter is boreal. Species of Alpheus are common 
in the tropics about coral-reefs; but the largest species of the 
genus, two or three inches long, occur beyond the tropics. 
lhe Penzidea, the lowest of the tribes of Macroura, are mainly 
tropical. Yet, the very lowest species (like the lowest Brachyura) 
occur partly in the colder waters, or even in the Frigid zone. 
XXII[. Comparing the torrid and temperate species of Ma- 
crowra, we are led to conclude, that the latter are probably most 
Numerous in individuals, and the most bulky in mass. Except- 
Ing the Panuliri, Scyllari, and some Paleemons, the tropical spe- 
cies are small, and moreover, they are not particularly abundant 
about coral-reefs. The species of the torrid genera, Pontonia, 
ipus, Harpilius, Anchistia, Paleemonella, Hymenocera, and 
Atya, are all quite small, the greater part not exceeding an inch 
and a quarter in length; moreover, the tropical Alphei are also 
small species, as stated above. The Penzidea are partly larger 
Species. Contrast these particulars with the facts as to the genera 
of the Temperate zone. Palinurus, Astacus, Nephrops, Parane- 
Phrops, Homarus, Arctus, Crangon and the related genera, Hip- 
Polyte, Pandalus, Cryphiops, contain species mostly of large size, 
and the adult Homari and Palinuri are not exceeded in weight 
by any other Macroura. 
The Thalassinidea, which belong almost exclusively to the 
temperate regions are smallest in the warmer part of the ‘Tem- 
Perate zone, and larger in the middle and colder part. A Puget 
ound species (subfrigid region) of Callianassa (C. gigas) 1s at 
least four and a half inches long, the C. uncinata of Chili, five 
Inches, and the Thalassina scorpionides of Chili, six inches. 
he facts respecting this subtribe, added to those mentioned 
above, strengthen much the conclusion, that the cold-water gen- 
€ra have the largest species ; for all the species are over an inc 
and a half in length. 
