264 MARINE INVERTEBRATES 



knobs, the third one being the most prominent, and forming the 

 posterior extremity when the abdomen is folded in. The walking- 

 feet are all simple and end in points ; the first pair are the longest, 

 and the following ones gradually diminish in size. The ventral 

 surface is rough and spiny. The abdomen is of about the same 

 length as the carapace. These animals are found off the Florida 

 coast and are caught in the fish-traps. They are uncommon. 

 The very peculiar development of the antennae makes them worthy 

 of examination when opportunity offers. 



ANOMALOUS FORMS: ANOMURA 



The anomalous forms which are intermediate between the sub- 

 orders Macrura and Brachyura were, until recently, placed in a 

 suborder, Anomura. The members of this group differ from one 

 another, and some of them resemble in external features mem- 

 bers of the other divisions of the suborders, but there is .a differ- 

 ence in anatomical structure which separates them in the classifi- 

 cation. 



FAMILY DBOMIDJE 



GENUS Hippoconcha 



H. arcuata. This curious little crab, found on the Florida coast, 

 carries the half of a bivalve shell over its back. Its fifth pair of thoracic 

 legs are bent over the back, and these, together with the fourth pair of 

 legs and the spiny front edge of the carapace, enable the crab to hold 

 the shell in position. This crab was formerly classed with the hermits, 

 all of which were originally called Berrihardus, after the monk of that 

 name. 



FAMILY PAGTTBIDJE 

 THE HERMIT-CRABS 



In these curious animals the posterior part of the body is not 

 protected by a crustaceous covering, and therefore the animal 

 seeks protection by inserting its soft and defenseless abdomen 

 into some hollow object, usually the shell of a gasteropod mol- 

 lusk, as the whelk or the periwinkle (Buccinum, lAttorina). 

 The hermit-crabs do not always use a shell for this purpose, 

 as they are sometimes found in the tubes of plant-stems or in 

 sponges. Like other organisms in the animal world, they seem 



