1818] CRUSTACEA OF THE UNITED STATES. 237 



all the feet are represented as didactyle; this, however, 

 was, it would appear, an error in the drawing. 



The name o{ fluviatilis, applied by this author to our 

 Penseus, is certainly not so appropriate as many others 

 which might be substituted, more especially as it is not 

 an inhabitant of fresh waters, as its name seems to indi- 

 cate, but is al way s found in salt or brackish water. Never- 

 thelessj as the name has been given, it would be presump- 

 tion of the most reprehensible kind in me to reject it, par- 

 ticularly as the species is actually found within the mouths 

 of rivers, probably as high up as the salt water extends. 



The sexes are distinguishable from each other by the 

 absence or presence of a connecting membrane to the an- 

 terior pair of natatory feet; the membrane is Formed by 

 the dilatation and junction of the inner appendages of 

 these parts. 



They appear in great numbers in the estuaries of the 

 southern states and Florida early in the spring, when they 

 are caught, to supply the markets, by means of a cast 

 net; the fisherman ascertains their presence in the water 

 at night, by the lines of light which are formed by their 

 darting amongst the phosphorescent molluscae, when a 

 splashing of the water, or the advance of a boat^ alarms 

 them. 



When recent, the colour is usually w^hitish, tinged 

 with reddish, and each side, particularly of the abdomi- 

 nal segments, with very pale greenish yellow, and sprink- 

 led in every part, except the eyes, tips of the caudal la- 

 mellae, pectus and venter, with small; radiate, reddish- 

 brown spots; eyes greenish, with dark moveable pupil; 

 caudal lamellae tipped with verdigrise green, cilia red; 

 antennae reddish, the dorsal carina of the fourth, fifth and 



Vol. I. R 



