INTRODUCTION. xlix 
very abundantly scattered over the whole world. Like 
Talitrus, Orchestia lives out of the sea, choosing moist 
places, but not burrowing a habitat for itself as Talitrus 
does. With us, Orchestia lives within the reach of the 
spray of the sea; but some species in the Southern Hemi- 
sphere live many miles inland, choosing terrestrial plants 
for their abode, sometimes at an elevation of fifteen hundred 
feet above the level of the sea. In these specimens the 
males, and, we believe, the males only, have some one 
or other of the joints of one of the posterior pairs of legs 
developed into a large internally concave scale, which, we 
believe, assists in retaining moisture, so that the branchial 
sacs may not suffer from desiccation. 
The genus Montagua appears to be wholly confined to 
the northern temperate latitudes, the species gradually 
diminishing in size as they approach the warmer seas. 
The close assimilation of this with Stegocephalus and 
Pleustes of the colder latitudes, is shown by the inter- 
change of certain parts in their structure. In Montagua, 
the superior antenne have no secondary appendage, 
neither have the mandibles a palpiform one, and the 
posterior pair of pleopoda terminate in a single ramus. 
Pleustes resembles Montagua in the former characteristics, 
but has the posterior pair of pleopoda terminating in two 
rami.  Stegocephalus resembles Pleustes in its charac- 
teristics, but it has a rudimentary appendage on the 
superior antenne. We have little doubt but that the 
others have also such an appendage in the larval con- 
dition, since it is a common feature in young Amphi- 
poda. Stenothoé,in the Southern Hemisphere, represents 
the Stegocephalide in the Northern, and agrees with 
Montagua in all important characters ; it differs in having 
avery large hand to the second pair of gnathopoda,—a 
doubtful generic character, in our estimation. 
d 
