22 Geographical Distribution of Crustacea. 
"The table shows that the torrid species, in one of the groups, 
average larger than the extra-torrid. "l'he cold-water Palinuridee 
are as large as the largest warm-water species, and will outweigh 
them; the cold-water Galatheidea, are ten times the average 
length of the warm-water; the Alpheine, Palamonine, and Pe- 
neide are at least as large in the temperate regions as in the torrid. 
"There is hence nothing in the tropies to balance the Astacidee, a 
group of large species, some of them gigantic ; nor the Crangonidze, 
nor Pandaline. 'lhegenus Palamon, in the 'T'orrid zone, averages 
larger than in the 'l'emperate, the ratio being 3:5 to 2:4; the for- 
mer amount being reduced to 2:3 for the Palemoninse, by the 
species of the other tropical genera, which are mostly quite small. 
Yet, taking the ratio of 3:5 to 2-4, it affects but little the balance 
against the T'orrid zone. 
As to bulk, also, the ''emperate zone probably has the prepon- 
derance; yet our data are less definite. In the Galatheidea, the 
cold-water species are not only ten times larger lineally (which 
implies at least eight hundred times cubically), but they are far 
more prolific, swarming in vast numbers where they occur.  ''he 
"Thalassinidea are more numerous in extra-torrid species than tor- 
rid, as well as larger in size. 'The Scyllaride are mainly trop- 
ical; but the species are not of common occurrence, compared 
with the Astacida, which abound every where, and these, as well 
as the Crangonidae and Pandalinz, are all temperate zone species. 
The Palemonine and Penaeide probably preponderate in the 
tropies, and this may be also true of the Alpheinz. "Taking a 
general view of the whole, and considering the fact, that the 
extra-torrid species rather outnumber the torrid, we believe that 
the deduction above stated 1s correct. 
In the T'etradecapoda, the number of species, the number and 
diversity of genera, the number of individuals, and the bulk, are 
all greater in the extra-torrid seas than in the torrid, as has been 
explained on a preceding page; and this is especially true of the 
Amphipoda. M. 
The tendency to spinose forms among the species of the colder 
temperate regions, or Frigid zone, has been remarked upon on 
page 9, as exemplified among the Gammaridea, the Crangonidz; 
Lithodes, and Maioids. 
