62 



NATURAL HISTORY OF ARTHROPODS. 



The CORYSTOIDEA are entirely absent from the eastern coast of our continent, 

 though present in all other seas. They have the antennulae and maxillipeds much as 

 in the Maioids, but differ in the longer antennae and the very short epistome or region 

 in front of the mouth. 



The LEUCOSOIDEA or Oxystomata are extremely narrowed in front, the ex- 

 ternal maxillipeds, when placed together, forming a triangle. The carapax is more or 

 less circular in outline, while the antenna are very small, and the epistome wanting. 

 In Dorippe we have a similar commensalism to those already noticed, one species of 

 this genus never being found without a sea-anemone ( Cancrisocia expansa) upon its 

 back, nor has this anemone ever been found except in this position. In Calappa the 

 sides of the body are expanded, while the two large claws, armed with strong spines 

 above, are carried closely applied to the front of the body. 



The CANCROIDEA or Cyclometopa agree with the Maioids in their mouth-parts, 

 while the body is broader and the antennula? are transverse. They are well divided 



into two families, according to their habits, - 

 the CANCRIDJE having the feet constituted for 

 walking, while in the PORTUNID^E the pos- 

 terior feet are flattened and thus converted 

 into efficient swimming organs. 



The genus Cancer, which is represented on 

 our eastern coasts by two species and by four 

 on the California!! shore, may be taken as the 

 type of the group. Our eastern species range 

 from Labrador to the Bermudas, and by a 

 curious mistake in nomenclature, the form to 

 which the name borealis is applied extends 

 further to the south and not so far to the north 

 as does the more' common Cancer irroratus. 

 Cancer irroratus delights in secluded places 

 under rocks, where it is safe from enemies and 

 the pounding waves, while the stouter, heavier 

 borealis disdains such protection, and occurs 

 in places where it is exposed to the force of 

 the waves. By many European naturalists these 

 two forms are confounded, though in reality 

 they are very 



FIG. 76. Megalops of common crab, Cancer 

 irroratus. 



distinct, the teeth of the margin of the carapax being 

 smooth in C. irroratus and crenulated in the other species. 

 The European Cancer pagurus is used as an article of 

 food both in England and upon portions of the continent, 

 while none of our forms have much economic use. The 

 genera and species of the Cancridae are very numer- 

 ous, especially in the warmer seas of the world, many 

 being conspicuous by reason of their bright colors, 

 though in habits no particular interest attaches to 

 them. The mud-loving Panopeus of the warmer 

 waters of both coasts of America is the only other 

 species to which our space will allow us to refer. 



tvr 



FIG. 77. Panopeits depressus, mud crab, 

 natural size. 



