TRACHOMEDUSAE 



119 



Fig. 199 — Microhydrn ryderi (Potts). 

 A, hydroid ; B, medusa. 



medusa which buds from the hydroid, bell-shaped, with 4 radial canals 

 and 8 tentacles: 1 species, in fresh water. 



M. ryderi Potts (Fig. 199). Hydroid cylindrical, with a crown of 

 nematocysts around the mouth, .5 mm. 

 long, often branched near the base 

 into two equal individuals; medusa .3 

 mm. high and .4 mm. wide at birth; 

 no sense organs or gonads observed: 

 on stones in rapid streams in Phila- 

 delphia ; Germany. 



3. Craspedacusta Lankester 

 {Limnocodium Allman). Trophosome: 

 minute, without tentacles. Gonosome: 

 disc-like medusa with 4 radial canals; 

 tentacles numerous, of several dif- 

 ferent lengths; lithocysts numerous; 

 manubrium long: 2 species; distribu- 

 tion world-wide. 



C. sowerbi* Lank. (Fig, 200). 

 Diameter about 12 mm.; gonads 4, 



suspended from the radial canals, greenish in color; oral lobes, large, 



crenulated, greenish; bell translucent 

 with a faint bluish tint ; 4 long, about 

 28 shorter and 192 shortest tentacles: 

 in a fresh-water aquarium in Wash- 

 ington containing tropical water lilies; 

 also in similar places in London, Mu- 

 nich, and Lyons; probably introduced 

 from South America. 



Family 2. AGLAURIDAE. 



Trophosome: wanting. Gonosome: 

 medusa with 8 radial canals, free 

 lithocysts and gonads in berry-like 

 masses and numerous tentacles: 5 

 genera. 

 Key to the genera of Aglauridae here described : 

 a, Gonads S. 



&i Gonads borne on manubrium 1^ Aglaura 



62 Gonads borne on radial canals 2. Aglantha 



«o Gonads 2 ^ Persa 



* See "Occurrence of Fresh-water Medusa, Limnocodiuni, iu the United States," 

 by C. W. Hargitt, Biol. Bull., Vol. 14, p. .304, 190S, 



Fig. 200 — Craspedacusta sowcrhi 

 (from Mayer). 



