Geographical Distribution of C'rustacea. 7 
X. If the 'T'orrid zone is the proper region for the full develop- 
ment of the Cancroid type, and its heat is needed for this end, it 
is natural that species of Cancroids like the Portunine, Platy- 
onychide, and Cancride, found in the less genial waters of the 
'Temperate zone, should bear some mark of inferiority ;—and it is 
a fact that they have such marks in their structure. This inferi- 
ority is not seen in their smaller size,—for a larger size under cer- 
tain conditions, may equally evince a lower grade,—but in the 
inferior concentration of the life-system, exhibited either in the 
lax outer maxillipeds, the elongation of the antennz and abdomen, 
or in the smaller size or swimming character of the posterior legs. 
F'or a like reason also, the species of Corystoidea, a grade still 
lower, naturally occur in the cold and ungenial region they fre- 
quent. 
We hence perceive, that the degradation among the Maioids 
takes place when the species become warm-water species, and the 
degradation among the Cancroids, in the reverse manner, when 
the species become cold-water species; for the reason that the 
colder waters are the proper habitat for the Maioid type, and the 
warmer for the Cancroid type. 
XL. In the tables of the Maioidea and Cancroidea of the 'T'em- 
perate and 'l'orrid zones, page 317, the species are included by 
families and subfamiles, and consequently the peculiarities of 
the genera are not shown. . In the families or subfamilies re- 
ferred to the cold-water section, there is only one warm-water 
genus, viz., JJoclea, of the subfamily Lébinine ; 1t contains four 
''orrid and one 'T'emperate zone species. 
Among those referred to the warm-water section, there are the 
following cold-water genera :— 
Species in Species in 
'Torrid zone. "l'emperate zone. 
Parthenopinea, genus Eurynome, 0 
d *  Eurynolambrus, 0 1 
Xanthidsze, *  Paraxanthus, 0 2 
Ozinz, *  Ozius, 2 8 
'The species of Cancrinea of the 'T'orrid zone section, which 
reach farthest into the ''emperate zone, are those of the follow- 
ing genera :— Xantho, which has eight ''emperate zone species 
out of twenty-eight in all; Panopeus, which in the same way: 
has four out of ten; Pilumnus, which has seven out of twenty- 
two; and Lupa, which has four out of ten. ''he cold 'l'emper- 
ate Region is the highest for each of these genera, excepting 
Lupa and Pilumnus, a species of each of these latter genera ex- 
tending just within the limits of the Subfrigid Kegion, on the 
coast of Massachusetts. 
. XH. 'The Grapsoidea, if divided between the 'T'orrid zone and 
'emperate zone, according to families or subfamilies, will fall 
within the 'l'orrid zone, excepting a single family of the Pinno- 
