TBACHOMEDUSAE 117 



and tentacles 80 to 100 in number: Greenland to North Carolina, the 

 southern variety being pink. 



Family 6. THAUMANTIIDAE. 



Trophosome: unknown, in most genera. Gonosome: medusa ocel- 



late and without lithocysts, with a short manubrium and usually 4 to S 



radial canals: about 14 genera. 



1. Melicertum Oken. Hydroid form minute; medusa bell-shaped; 



8 radial canals and numerous long tentacles with ocelli at their base: 



4 species. 



M. campanula Agassiz. Color of medusa light ochre, tentacles and 



gonads darker; manubrium short ^vith convoluted lobes; height and 



diameter 2 cm.: Cape Cod to Greenland, 



often abundant; Europe. 



2. Laodicea Lesson {Lafoea Lamou- 



roux). Hydroid an unbranehed colony with 



Fig. 197— Laodicea calcarata ^ filiform hydrorhiza; hydrothecae tubular; 

 (Hargitt). -^ . . 



gonangia oblong, often forming encrusting 



masses around the stem; medusa hemispherical when young, but flatter 

 as adult, with 4 radial canals and numerous tentacles, with basal cirri 

 and ocelli: G species. 



L. calcarata A. Agassiz (Fig. 197). Hydroid form usually parasitic 

 on sertularians ; medusa transparent with 2 tentacles at birth, but many 

 later, which are quite rigid; manubrium short, with fluted sides; diam- 

 eter 25 mm. : Massachusetts Bay to Florida. 



Order 5. TRACHOMEDUSAE. 



Trophosome: wanting in most forms, so far as known; where pres- 

 ent, of minute size and allied apparently to the Tubulariae. Gonosome: 

 free medusae, usually rather large, more or less bell-shaped, with a 

 velum and 4, 6, or 8 radial canals, along which on the subumbrella are 

 the gonads; manubrium usually long, often extending beyond the velum; 

 tentacles often very long and sometimes springing from the exumbrella; 

 lithocysts with concretions of entodermal origin and either freely pro- 

 jecting or enclosed in pockets; development apparently direct in most 

 cases, without alternation of generations, the animals being essentially 

 open-ocean animals, most of which are not bound to the shores by a 

 hydroid generation, and where the latter is present it is apparently in a 

 degenerate condition: 5 families end 80 species. 



