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 antenne 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 DROME 
Genus Hippoconcha 
HI. arcuata. This curious little crab, found on the Florida coast, 
earries the half of a bivalve shell over itsback. 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 Bernhardus, after the monk of that 
name. 
FAMILY PAGURIDE 
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, Littorina). 
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 
