DEVELOPMENT OF THE EOCK CEAB. 767 



but symmetrically arranged mammillations, some of which are scarcely defined. The surface 

 appears nearly smooth, but is really covered with closely-placed, minute granulations. The eyes 

 stand on short, stout peduncles, which lie in deep circular holes on either side of the middle of 

 the front margin. Between the eyes there are three small teeth, and on each side, between the 

 eyes and the outer edge of the shell, the margin is indented to form nine broad and stout teeth. 

 The claws are rather short and stout, the inner margins of the fingers bearing each a row of 

 few, large, blunt, and sometimes double tubercles. The four posterior pairs of legs are similar 

 to one another, long and slender, with pointed tips. The ground color of the carapax is yellowish, 

 closely dotted with dark purplish-brown, which becomes a reddish-brown after death. 



The only species of Crab upon our Atlantic coast which could possibly be confounded with 

 the present one is Cancer horealis, of which a description is given following this. The differences 

 between the two species being once pointed out, there is no difllculty in distinguishing between, 

 them. 



Economic value. — The Eock Crab is not much in demand as an article of food. It is sold 

 to some extent in the markets at Boston, New Bedford, Newport, New York, and perhaps 

 elsewhere within the limits of its range, generally, if not always, in a hard-shell condition. 

 But even in Boston, where it could be easily supplied, its place is mainly taken by the common 

 edible Blue Crab {CalUnectes hastatus), which is sent there fresh from New York and other 

 localities. The two species of Cancer are, however, more nearly related to the English edible 

 Crab {Cancer pagurus) than is our. own common edible Crab, and, were this kind of food more 

 appreciated by the American seacoast inhabitants, there is no reason why the Eock Crab, as 

 well as the "Jonah," should not be utilized to a very great extent. In some places, Newport 

 for instance, the two species of Cancer, but especially the Cancer horealis, aie preferred to. the 

 CalUnectes hastatus, but this is not the rule elsewhere. 



Development. — The following account of the growth and development of this Crab, by 

 Prof. S. I. Smith, will suffice, in a general way, for nearly all the American species of Crabs, and; 

 will serve to indicate the curious, changes which take place before the simple crab egg becomes a 

 well-developed Crab. Such an account as this becomes very valuable in many cases as a means of 

 pointing out the essential 4etails to be followed in the artificial breeding of marine animals. 



"AU^ or at least nearly all, the species of Crabs living on the coast of New England pass. 

 through very complete and remarkable metamorphoses. The most distinct stages through which 

 they pass were long ago described as two groups of crustaceans, far removed from the adult forms 

 of which they were the young. The names Zoea and Megalops, originally applied to these groups,, 

 are conveniently retained for the two best marked stages in the development of the Crabs. 



"The young of the common Crab [Cancer irroratus), in the earlier or zoea stage, when first 

 hatched from the egg, are somewhat like the form figured [reproduced on one of the plates at the 

 end of this volume], but the spines upon the carapax are all much longer in proportion, and there 

 are no signs of the abdominal legs or of any of the future legs of the Megalops and Crab. 

 In this stage they are very small, much smaller than in the stage figured. After they 

 have increased very much in size, and have molted probably several times, they appear as in 

 the figure just referred to. The terminal segment of the abdomen, seen only in a side view in the- 

 figure, is very broad and divided nearly to the base by a broad sinus; each side the margins 

 project in longj spiniform, diverging processes, at the base of which the margin of the sinus i» 

 armed with six to eight spines on each side. When alive they are translucent, with deposits of 

 dai^ pigment forming spots at the articulations of the abdomen and a few upon the cephalothorax 

 and its appendages. In this stage they were taken at the surface in Vineyard Sound, in immense' 



