Geographical Distribution of Crustacea. 319 
X. If the Torrid 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 antenne and abdomen, 
or in the smaller size or swimming character of the posterior legs. 
For a like reason also, the species of Corystoidea, a grade still 
lower, naturally occur in the cold and ungenial region they fre- 
quent. 
perate and Torrid 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., Doclea, of the subfamily Libinine ; it contains four 
Torrid and one ‘Temperate zone species. 
Among those referred to the warm-water section, there are the 
following cold-water genera :— 
Species in Species in 
Torrid zone. Temperate zone. 
0 eo 
Parthenopinea, genus Eurynome, 4 
° “ Eurynolambrus, 0 1 
Xanthide, “ Paraxanthus, . 0 2 
Ozine, ius, . 2 3 
The species of Cancrinea of the Torrid zone section, which 
teach farthest into the Temperate zone, are those of the follow- 
Ing genera :— Xantho, which has eight Temperate zone species 
cut 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. The cold Temper- 
ate Region is the highest for each of these genera, excepting 
Upa and Pilumnus, a species of each of these latter genera ex- 
tending just within the limits of the Subfrigid Region, on the 
Coast of Massachusetts. : 
XIL The Grapsoidea, if divided between the Torrid zone and 
emperate zone, according to families or subfamilies, will fall 
Within the Torrid zone, excepting a single family of the Pinno- 
