CAMPANULARIAE 



113 



Key to the genera of Eucopidae here described (hydroid form well 

 known in Obelia and Clytia alone) : 



G! Manubrium of medusa short ; hydroid mostly a branching colony. 

 ^Medusa flat and disc-like ; hydroid a branching colony ; hydrotheca often 



without a toothed margin 1. OBELIA 



& 2 Medusa bell-shaped or hemispherical. 

 G! Medusa with no more than 16 marginal tentacles. 

 di Medusa without cirri at the base of the tentacles; hydroid not or very 



sparsely branched ; hydrotheca with toothed margin 2. CLYTIA 



<, Medusa with 4 or more tentacles, each of which has 2 basal cirri. 



4. EUCHEILOTA 



c 2 Medusa with more than 16 tentacles. 



diOral lobes frilled 3. TIABOPSIS 



d 2 Oral lobes not frilled 5. OCEANIA 



03 Manubrium of medusa very long; hydroid mostly unknown. 



6i Tentacles 4 6. EUTIMA 



e 2 Tentacles of adult numerous 7. TIMA 



1. OBELIA Peron and Lesueur. Hydroid colony usually branched, 

 the stem with annulations at the base of the branches and the hydranths ; 

 hydrotheca often with * untoothed margin; gonangium 



with a small terminal ^K" /* aperture, usually surrounded by 

 a collar or neck; me- %(PJ^ dusa more or less disc-shaped, 1 



to 6 mm. in diameter, j( \i with 12 or more marginal 



tentacles and 8 (P|\ | J^|?k lithocysts, often swim- 



ming with everted ^o^W/ Jp^=^ bell: numerous species, 



Fig. 187 Obelia dichotoma (Mayer). A, entire colony; B, colony enlarged; C, 



medusa. 



the medusae of which can often not be distinguished from one 

 another. 



0. commissuralis McCrady. Colony tree-like with long central trunk, 



15 to 20 cm. high, sparsely branched, the side branches springing out at 

 right angles; hydrotheca not toothed; gonangia elongate; medusa with 



16 or more tentacles: on docks, algae, etc., from South Carolina to Bay 

 of Fundy; common; California. 



0. dichotoma (L.) (Fig. 187). Colony rather small with a deep 

 brown stem and a general tree-like appearance; branches zigzag; hydro- 

 theca elongate without toothed margin; gonangia long and conical; 



