PARATANAIS RIGIDUS. 



ISOPODA. 



ABERRANT/A. 



141 



TANAID^E. 



PARATANAIS RIGIDUS. 



Specific character. — Body narrow. Margins of the pereion and pleon 

 parallel, pleon terminating in a central point. Antennre not longer than the 

 cephalon. Posterior pleopoda having both rami uniarticulate, the outer 

 being half the length of the inner. 



Length ^th of an inch. 



The form of this species is slender and cylindrical, 

 the sides running parallel with each other from the outer 

 angle of the anterior margin of the head almost to the 

 posterior pair of pleopoda. The cephalon is confluent 

 with the first segment of the pereion, and both together 

 form a segment that is scarcely longer than broad. The 

 second segment of the pereion is very short ; the third is 

 about three times as long as the second, and both together 

 about as long as the cephalon ; the fourth segment is 

 quadrate, and as long as the two preceding ; the fifth is a 



