^B. alata.^ Slightly oval in form; lower part of the body divided into two large lobes which hang below the mouth. Four of the swimming-plates are shorter than the other four and terminate in curious processes or short appendages called auricles. /Bolina/ is about two inches in length, and is very delicate, transparent, and phosphorescent. Its contractile power enables it to vary in outline to a considerable extent. It has a slow undulating motion, and sometimes carries its lobes uppermost and open. Usually found associated with /Pleurobrachia/ from Massachusetts northward. ^B. septentrionalis.^ Found on the northern Pacific coast. ^B. vitrea.^ A species found in Florida. [pg157] 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. /Cestum/ 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 difficult to capture it uninjured. Its habitat is the Mediterranean Sea. It may be seen among the zoölogical specimens in almost any museum. [Illustration: /Cestum veneris./] ORDER =BEROÏDA= GENUS ^Idyia^