COMB-JELLIES 157 
Genus Mnemiopsis 
_ M. Leidyii. Resembles Bolina in general form; often six to eight 
inches in length; gregarious, thousands often being collected together ; 
exceedingly phosphorescent. 
ORDER CESTIDA 
Genus Cestum 
C. veneris, Venus’s girdle. This singular animal, although not an 
inhabitant of our seas, has its place in this group, and is shown here 
because of its very curious shape. In form it is flat and ribbon-like. 
Sometimes it attains a length of five feet, while in breadth it is but one 
or two inches. The mouth is midway in its length and is opposite the 
sense-organ or eye-spot. On each side of the mouth is a short tentacle 
which protrudes from a sac. Four of the swimming-plates are small; 
the other four extend along the edge of the body. Cestwm moves by 
contractions of the body more than by the combs which fringe its edges. 
It is very transparent, with a violet hue, and is so delicate that it is diffi- 
cult to capture it uninjured. Its habitat is the Mediterranean Sea. It 
may be seen among the zodlogical specimens in almost any museum. 
ORDER BEROIDA 
Genus Idyia 
I. roseola. This species has an ovate body three to four inches in 
height and about half as broad. Some individuals are larger. It has 
Cestum veneris. 
