4818.] OF TME UNITED STATES. 389 



•simple, with two minute hooks at tip, posterior pair 

 longest; coxa simple or not remarkably dilated; abdo- 

 men of three segments; natatory feet with the filaments 

 subequal; tail of three segments, the first and second 

 bearing each a pair of bifid styles, terminal one suborbi- 

 cular, with a pair of simple, depressed styles, concealed 

 ky the others. » 



SPECIES. 



M. irrorata'^. Eyes hemispherical; hands of the an- 

 terior feet with a longitudinal palm, and prominent tooth, 

 ^ose of the second pair compressed, ciliated. 



Inhabits Eggharbour. 



Cabinet of the Academy. 



Accessory seta of the superior antennae attaining the 

 fifth articulation of the terminal joint; eyes conspicuous, 

 rounded; palm of the anterior feet a little convex in the 

 middle, a large obtuse tooth at base; nail attaining the 

 carpus, which terminates so as to appear hke a second 

 tooth of the hand; second pair of feet ciliated, with a 

 subtriangular hand, segments of the abdomen mucronate 

 each side behind; colour when recent, pale with very nu- 

 merous red points. 



Length three tenths of an inch. 



Not being able to refer this animal to any existing 

 genus, I was induced to frame the present genus for its 

 reception. It approaches Gammarus by having the ac- 

 cessory seta to the superior antennae, but is excluded 

 from that genusj, and its congeneers, such as Talitrus, 

 Dexamine, Leucothoe, &c., by the absence of the enlar- 

 ged lamellated coxae, which are so conspicuous in those 

 genera. To the genus Pherusa it seems to approach by 

 Vol. I. K k 



