Ul8.] CRUSTACEA OF THE UNITED STATES. 251 



spined on each side at the edge, of which one is placed 

 above the other; third and iourth segments entire over the 

 insertion of the coxae of the feet, mucronate; fifth segment 

 somewhat rounded over the insertion of the posterior feet, 

 where it is partially concealed by a small squamiform 

 appendage, which is attached by a suture to the first joint 

 of the abdomen; thumb armed on the inside with five, 

 long, permanent spines, and terminated in a similar, but 

 more elongated one, all received at tip in corresponding 

 cavities of the anterior edge of the hand; Aan(/ elongaied, 

 thickened, pectinated on the anterior outer edge, parallel 

 with the recipient cavities, three moveable spines near 

 the base, inflected, so as to meet the terminal spines of 

 the thumb; third or principal joint, unarmed; carinated 

 line behind the anus very short. 



Length of the female four and a half inches, male two 

 and three quarter inches. 



This fine species was found by Mr. Le Sueur on the 

 coast of Rhodeisland, and was presented by him to the 

 Academy. The very striking resemblance which it bears 

 to the S. mantis has hitherto caused it to be confounded by 

 naturalists with that species. But an attentive examination 

 of its characters, and a comparison of them with those of 

 the species just meiitioned, will convince us that it is per- 

 fectly distinct. I will, in this place, briefly mention two 

 or three differences, which of themselves are sufficient to 

 justify a separation of the American species. The large 

 plate of the thorax, in the foreign specimen of S. mantis 

 under examination, is perfectly simple over the coxae of 

 the large feet or arms, whereas in our species, that part is 

 extended into an angle; the next segment is, it is true, 

 two- spined on each side in the European animal, but 



