354 REPORT OF NATIONAL MUSEUM, 1892. 



Members of many of the families of the large subclass Malacostraca 

 range beyond the limits of marine waters, but most of them are con- 

 fined to a marine habitat. 



The living Brachyurans are so generally of marine habitat that in the 

 absence of any conflicting evidence geologists are usually disposed to 

 regard all those strata as of marine origin which contain fossil remains 

 referable to this division of the Crustacea, but the following facts show- 

 that this exclusive view is not admissible. The greater part, if not all 

 of one subfamily, the Thelphusinia, are either denizens of Iresh waters 

 or live a large part of the time upon the land in the vicinity of fresh 

 waters. Some species of the Grapsoidea, although most of them are 

 marine, also have a similar range and peculiarity of habitat while 

 others are apparently confined to brackish waters. Many of the marine 

 as well as of the fresh-water species of the Grapsoidea range more or 

 less upon the land. 



Although it is well to emphasize the fact that most of the species 

 and genera of the Brachyurans are typically marine animals, many of 

 them besides those already referred to, such, for example, as the genera 

 Oallinectes and Panopeus, range into estuaries and bays, some of them 

 going into adjacent fresh waters without apparent inconvenience. It 

 is also a signittcant fact that of the Brachyurans, as well as of the 

 Macrurans which inhabit fresh waters, many more are found in flnvia- 

 tile and palustral than in lacustrine waters. 



The range of habitat of the Anomoura is similar to that of the Brach- 

 yura. Most of them live in waters of full marine saltness, some 

 inhabit brackish waters, some wander inland, and one genus, iEglea, 

 is nearly or quite confined to fresh waters. It is thus apparent that 

 the discovery of fossil remains of a representative of this group of Crus- 

 taceans in a given formation would not necessarily be proof of its marine 

 origin. 



The Macrura as a whole have a wide range of aquatic habitat, most 

 of them living in marine waters, many in fresh waters, and some of 

 them venturing occasionally upon the land. 



The family Astacidse proper, or crayfish, are all denizens of fresh 

 water, while those similar genera which were formerly referred to this 

 family are confined to a marine habitat, with the probable exception 

 that some of them range into brackish waters. Although many of the 

 Astacida? burrow in wet earth at considerable distances from any body 

 of water, few or none of them wander so far upon the land as do some 

 of the Brachyura or even some of the Anomoura. 



The Crangonida- are generally of marine habitat, but some range into 

 brackish waters. 



Most if not all the Atyidre inhabit fresh waters. 



Many of the Pahemonidie are restrictei to marine waters, many live 

 in brackish waters, and several genera are confined to fresh waters, 

 some of them living in rivers far from the sea. 



