Geographical Distribution of Crustacea. | 13 
while the other legs are vergiform, shows a relation to the Brach- 
yura, which is evidence of superiority. "'l'hese Crangonidee, thus 
the highest of the Caridea, are almost exclusively cold-water 
. Species. 
In the family Paleemonidze, some genera have the anterior legs 
furnished with stout hands, while in others the second is the 
stout chelate pair. 'l'he former, for the reason just alluded 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 Alpheinze, that we find the cold-water and 
boreal species. 'lT'he genus Hippolyte alone contains thirty-seven 
eold-water species, nineteen of which are of the F'rigid zone; 
and there are only eight torrid species. 
On the contrary, among the Palemonine, 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 tropies about coral-reefs; but the largest species of the 
genus, two or three inches long, occur beyond the tropics. 
'The Penzidea, the lowest of the tribes of Macroura, are mainly 
tropieal. Yet, the very lowest species (like the lowest Brachyura) 
occur partly in the colder waters, or even in the F'rigid zone. 
XXIII. Comparing the torrid and temperate species of Ma- 
eroura, 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 Palemons, the tropical spe- 
cies are small, and moreover, they are not particularly abundant 
about coral-reefs. "Tl'he species of the torrid genera, Pontonia, 
C(Edipus, Harpilius, Anchistia, Palemonella, Hymenocera, and 
Atya, are all quite smáll, the greater part not exceeding an inch 
and a quarter in length; moreover, the tropical Alphei are also 
small species, as stated above. "The Peusidea are partly larger 
species. ' Contrast these particulars with the facts as to the genera 
of the ''emperate 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 'T'halassinidea, which belong almost exclusively to the 
temperate regions are smallest in the warmer part of the 'l'em- 
perate zone, and larger in the middle and colder part. .A Puget 
Sound species (subfrigid region) of Callianassa (C. gigas) is at 
least four and a half inches long, the C. uncinata of Chili, five 
inches, and the 7'halassina scorpionides of Chili, six inches. 
'The facts respecting this subtribe, added to those mentioned 
above, strengthen much the conclusion, that the cold-water gen- 
era have the largest species; for all the species are over an inch 
and a half in length. 
