434 CRUSTACEA [November, 



Inhabits northern coast of the United States, very 

 common. 



Cabinet of the Academy, Peak's Museum. 



Thorax subkmatc, truncate at its junction with the 

 abdomen, convex, margined on its outer and anterior 

 edge, acute and elongated at the hind angles, seven sub- 

 equal reflected spines on the disk, of which six are 

 placed on two parallel, transverse lines, and transversely 

 equidistant, posterior line on the edge of the truncature, 

 lateral anterior ones bearing the eyes on their exterior 

 side, seventh spine anterior and distant from the other, 

 supporting two stemmata; eyes longitudinally oval; feet^ 

 second joint of the four anterior pairs, armed beneath 

 with four or six moveable spines, of which two of three 

 are approximated at tip, and two or three distant and 

 placed longitudinally, second joint of the hind pair, with 

 about two moveable spines and a much larger one at the 

 inferior tip of the fourth joint; abdomen depressed, a lon- 

 gitudinal line of three, elevated, somewhat reflected spines, 

 smaller than those of the thorax, anterior one placed at 

 the base, intermediate one behind the middle, posterior 

 one at tip over the insertion of the tail, lateral angles of 

 the base elevated into a dilated, compressed, oblique 

 spine, lateral edge with twelve alternately permanent and 

 moveable spines, of which the latter are longer, hind an- 

 gles elongated each side of the origin of the tail and 

 acute; tail serrate above with from twenty to thirty spine- 

 like teeth, which are unequal, inequidistant and shorter 

 than one-fourth of the transverse diameter of the tail. 



Length to the end of the tail, female nearly two feet, 

 male about twenty inches. 



The male differs from the female in being smaller. 



