INTRODUCTION. xlix 



very abundantly scattered over the whole vrorld. 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 

 Plenstes of the colder latitudes, is shown by the inter- 

 change of certain parts in their structure. In Montagua, 

 the superior antennje 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 iu 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 antennae. 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. Stenothoe, in the Southern Hemisphere, represents 

 the StegocephaUdce in the Northern, and agrees with 

 Montagua in all important characters; it differs in having 

 a very large hand to the second pair of gnathopoda, — a 

 doubtful generic character, in our estimation. 



d 



