116 CCELENTERATA 



Family 5. ^QUOREIDAE. 



Trophosome: mostly unknown. Gonosome: medusa often of large 

 size and more or less disc-shaped, with from 8 to 100 radial canals; 

 gonads usually ribbon-like; 8 or more lithocysts; 8 or more marginal 

 tentacles: about 7 genera. 



Key to the genera of ^quoreidae here described : 



Oi Manubrium short. 



&i Radial canals 8 to 20 1. Halopsis 



6o Radial canals 16 to 100 2. ^quorea 



fla Manubrium large and long 3. Zygodactyla 



1. Halopsis A. Agassiz. Medusa disc-like in adult and hemispher- 

 ical in youth; radial canals 12 to 20 in 4 groups; marginal lithocysts, 



tentacles and cirri numerous ; 

 manubrium short with 4 oral 

 lobes: 1 species. 



H. ocellata A. Ag. Di- 

 ameter 7 cm.: New England 

 coast; rare. 

 ^ ^)v' 2. ^QUOREA Peron and 



Fig. ISi^-^quorea tenuis (Mayer). Lesueur. Hydroid form mi- 



nute and mostly unknown; 

 medusa disc-shaped or hemispherical, with a short, wide manubrium 

 and numerous radial canals, lithocysts, and tentacles: 10 species. 



A. {Rhegmatodes A. Agassiz) tenuis 

 A. Ag. (Fig. 195). Radial canals 20 to 

 40 with an equal number of gonads; ten- 

 tacles numerous, long and slender, with a i¥;?\\ivv\\r«Arf 

 spur above the base of each; diameter 3 ^;1i]I4J^WnI 

 to 10 cm. : Vineyard and Long Island ^^=-^1 \^ 

 Sounds; veiy irregular in its occurrence. 



A. albida (A. Ag.) Radial canals 

 and tentacles 80 or more in number; 

 above each tentacle is a spur; diameter 7 

 cm. : New England coast. 



3. Zygodactyla Brandt. Hydroid 

 form unknown; medusa arched and with 

 a large sac-like manubrium with exten- Fig. we—Zi/fjodactyia grcenlan- 

 sive frilled oral lobes extending bej^ond 



the velum; subumbrella with rows of warts between the radial canals: 

 1 species. 



Z. grcenlandica (Peron and Lesueur) (Fig. 196). The largest Amer- 

 ican hydromedusan, measuring 12 cm. or more in diameter; radial canals 



