THE CRUSTACEA OF NEW JERSEY. 237 



Super-Family ASELLOIDEA. 



The Asels. 



All segments of metasome fused together to form more or 

 less broad shield-like plate, the caudal segment. Pleopoda wholly 

 without swimming-power, exclusively branchial in character, 

 and in considerably reduced number. Usually first pair trans- 

 formed to single opercular plate, and to protect extremely deli- 

 cate succeeding pairs this operculum in male peculiar. Uropoda 

 terminal, never form part of caudal fan, or being of valvular 

 character. Though appendages of metasome quite unserviceable 

 for locomotion, some forms are expert swimmers. This is 

 effected by aid of three posterior pairs of legs being modified 

 as oar-like swimming- implements, by strokes of which the animal 

 is propelled backwards. Form of body greatly variable, some- 

 times very broad and depressed, sometimes slender and elon- 

 gated, approaching to a cylindrical shape. Cephalon always 

 well defined, mesosome showing normal number of segments 

 which sometimes form into two rather distinct sets by means of 

 a median constriction. Coxal plates very small or cpiite obsolete, 

 never forming marginal area. Superior antennae generally 

 smaller than inferior, which sometimes attain an excessive 

 length. Oral parts normal. Only first pair of legs assume a 

 subchelifomi structure. 



Family ASELLID.^. 



The Asels. 



Body more or less broad, depressed, with lateral parts of seg- 

 ments lamellar. Cephalon of moderate size, without any 

 rostrum, lateral parts scarcely expanded. Caudal segment large. 

 Shield-like eyes, when present, small and lateral. Both pairs of 

 antennas with multiarticulate flagella, superior ones much smaller 

 than inferior and issuing close together. Oral parts normal. 

 Legs ambulatory, except first pair, which distinctly subcheliform. 



