CAMPANULARIAE 



113 



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

 known m Ohelia and Chjtia alone) : 



Oi Manubrium of medusa short; hydroid mostly a branching colony. 

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



without a toothed margin 1. Obelia 



62 Medusa bell-shaped or hemispherical. 

 Ci Medusa with no more than 10 marginal tentacles. 

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



sparsely branched ; hydrotheca with toothed margin 2. Clytia 



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



4. EUCHEILOTA 



Cz Medusa with more than 16 tentacles. 



diOral lobes frilled 3. Tiabopsis 



d. Oral lobes not frilled 5. Oceania 



tta Manubrium of medusa very long ; hydroid mostly unknown. 



61 Tentacles 4 6. Eutima 



en 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 ^^^ /a aperture, usually surrounded by 



a collar or neck; me- ^sMP" <i^sa more or less disc-shaped, 1 



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



tentacles and 8 (#^ 1 ,,^^ lithocysts, often swim- 



ming with everted ^^'Sj ^^^>^!^ ^®^^- numerous species, 



Fig. 187 — Ohelia dichotoma (Mayer). A, entire colony 



medusa. 



colony enlarged; C, 



the medusae of which can often not be distinguished from one 

 another. 



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



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; 



