138 NEW YORK STATE MUSEUM 



or the last pair may be flattened to form a finlike organ. The 

 abdominal appendages are much reduced, two pairs being found in 

 the male and one in the female. 



The eggs, which are usually much smaller in proportion than in 

 the Macrura, are carried attached to the hairs of the abdominal 

 appendag-es of the female. The young are hatched in a form very 

 different from the adult and known as a zoea. It is a free- 

 swimming form, characterized by the presence of but two pairs of 

 legs, which represent the second and third pairs of maxillipeds- of 

 the adult. The other appendages appear gradually at the successive 

 molts of the animal, though up to a certain stage it still retains the 

 zoea form. At that molt, however, it suddenly changes, attaining 

 a form very similar to that of the adult, but with the abdomen held 

 straight out behind instead of flexed. This is known as a megalops 

 and by a further series of molts it attains the definitive crab form. 



This order includes the crabs, among which the blue, or edible 

 crab is familiar to everyone. Besides this, the large lady crab, the 

 green crab and the spider crabs are found, walking over the bottoms 

 of the bays or concealed under the seaweeds. Small mud crabs are 

 found under stones in muddy situations, and the odd looking fiddler 

 crabs occur on the marshes. 



Keys to the Brachyura of North America by Mary J. Rathbun 

 are to be found in the American Naturalist, 1900, v.34, as follow: 

 " Cyclometopous or Cancroid Crabs," p.131 ; *' Oxyrhynchous and 

 Oxystomatous Crabs," p. 503 ; " Catometopous or Grapsoid Crabs," 



p.583. 



The Brachyura are divided into four tribes : i Cyclometopa, 

 2 Oxyrhynca, 3 Catometopa, 4 Oxystomata. 



These may be separated by the form of the carapace and the front, 

 that is the portion between the eyes. The Oxystomata are not 

 represented. 



T CYCLO^IETOPA 



Cancroid crabs. Carapace usually broader than long and reg^u- 

 larly arched in front. No rostrum. 



Divided into three families, Cancridae, Pilumnidae and Por- 

 tunidae, all of which are represented. 



