$5 Geographical Distribution of Crustacea. 
- IThe Lithodea belong to the coldest temperate regions, abound- 
ing especially in the subfrigid region.  'l'he Galatheidea ar 
mainly. of the temperate zone; there are five known torri 
ejes, and seven temperate, the latter pertaining to the colder. 
"The genus Porcellana has but two-thirds as many speci 
the temperate as in the torrid zone. Yet the subtemperate | 
contains but one less than the subtorrid, and some of the 
species of the genus occur here; while, on the contrar 
torrid-zone species are quite small. Although, therefore, Po 
lana may rank as a torrid zone genus, if we consider the relative 
number of species in the two zones, it is more properly a tem- 
 perate zone genus. 
'The Paguridea range through both the tropics and temperate. 
zone, even passing into the frigid zone. Bernhardus is mainly 
a cold-water genus, while Pagurus, Calcinus, and Clibanarius are 
mostly torrid genera. asgurus has seven out of twenty-one 
species in the temperate zone. But it is in the torrid zone where 
" the species of the largest size occur; the extra-torrid species be- 
long almost exclusively to the Mediterranean. "Phe species are 
exceedingly prolific in the tropics, far exceeding what occurs as 
regards any Paguridea in the temperate zone. 
XVIII. It was found in the Brachyura, that the highest spe- 
cies among the Maioids, and the highest of Crustacea occur in 
the eztra-tropical regions; aud that as we descend to the Can- 
croids, the species become mainly íropical; moreover, as we 
descend among the Cancroids (the type of which is tropical), 
there is in general a return to the less genial colder waters, as 
exemplified in the true Cancers or Caneridae and the Corystoidea, . 
these last being mainly cold-water species. By these steps we 
find the more degraded forms among the Brachyura occurring in 
both the colder and warmer waters. "We cannot therefore ex- 
pect that the Anomoura, which are properly. Brachbyura of a still 
lower grade, should be arranged according to rank 1n one zone in 
preference to the other. And it 1s a fact that the genera of higher 
species occur about equally in the two zones.  Latreillia, but a 
single step below the Inachidz, is found in the warmer temperate 
regions; and Dromia, a. little lower, has three-fourths of its spe- 
cies 1n the tropics.  Homola, again, has been found only in the 
temperate zone. 
Among the Paguridea, the Bernhardi or cold- water species are 
probably the superior in rank ; aud the Lithodea, which are a 
grade higher still, are from the neighborhood of the frigid zone. 
"The Hippidea, which we have considered as in the Corystoid 
series, but below the Corystoidea, are mostly from warmer waters. 
'The most bulky forms among the Anomoura are found in the 
genera Lithodes, Ranina, and Dromia. 'l'he common Aan»na 
dentata has a length of five inches in the Japan Seas, while iu 
