DYNAMENE. 417 



ISOPODA . SPHMROMIDA!. 



NORMALIA. 



Genus DYNAMENE. (Leach.) 



Generic character. Smooth, not bristly ; contractile into a 

 ball, with the lateral appendages of the pleon exposed ; 

 terminal segment having a deep excavation in the middle of 

 the posterior margin. Superior antenna with the basal joint 

 oblong, not flattened, and the second joint sub-triangular. 



THE species of this genus have much the appearance 

 of small Sphaeromse, but are distinguished from them 

 by the slit at the extremity of the tail, which is simple, 

 without a central tooth, as in Cymodocea, from which 

 they also differ in the smooth clean aspect of the dorsal 

 surface, and in the structure of the basal joints of the 

 superior antennae. 



The body is very convex, smooth, and destitute of the 

 bristles which are so conspicuous in the Cymodocese. 

 The upper antennae, when at rest, are concealed beneath 

 a slightly produced margin to the front of the head ; the 

 basal joint is oblong and but slightly flattened, the 

 second joint is triangular-shaped, and the flagellum is 

 multiarticulated ; the lower antennae are more slender at 

 the base than the upper, with four nearly equal basal 

 joints, and a moderately long multiarticulate flagellum. 

 The mandibular appendage has the two terminal joints 

 subequal and strongly setose on the inner edge ; the apex 

 of the mandible is armed with several minute denticulated 

 teeth and a slender setigerous lobe in the middle of the 

 apical edge; the foot-jaws have the intermediate joints 



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