CAMPANULARIAE 105 



the medusoid generation and may either be liberated as free medusae, 

 or, remaining- in the gonangium, produce the sexual products there, 

 ^hich escape from the gonangium as free larvae. The medusae 

 (Fig. 191) are known as Leptomedusae and (except in the Thauman- 

 tiidae) have lithocysts and not ocelli as sense organs: they bear the 

 gonads beneath the radial canals on the subumbrella: about 8 families. 

 Key to the families of Campanularkie here described : 



A. THE HYDROIDS. 



Ci Hydrothoca sessile, i. e., not joined to the stem by a stalk ; gonangium contains 

 sporosacs. 

 hi Hydrothecae in 2 rows (except HydraUmania) either opposite to each other 



on the stem or not 1. Sertulariidae 



&2 Hydrothecae in a single row on the stem 2. Plumulariidae 



fla Hydrotheca stalked and bell-shaped, 



6i The gonophores are sporosacs 3. Campanulariidae 



62 The gonophores are medusae ; hydroid forms very little known except in the 

 genera Obelia, Clytia, and Laodicca. 



4. EUCOPIDAE. 5. ^l^QUOREIDAE. 6. Thaumantiidae 



B. THE MEDUSAE. 



The 1st, 2nd. and 3d families produce only sporosacs and no free medusae. 



Oi Four simple radial canals; lithocysts and no ocelli present 4. Eucopidae 



02 Radial canals numerous (8-100) .• 5. x^quoreidae 



ci.j Radial canals 4 or 8 ; ocelli present and no lithocysts. .6. Thaumantiidae 



Family 1. SERTULARIIDAE.* 



Trophosome: colony usually branching; hydrothecae sessile (not 

 stalked), almost all with opereula (Fig. 173) and forming two rows 

 along opposite sides of the hydrocaulus (except HydraUmania). Gono- 

 some: gonangia much larger than the hydrothecae, there being only a 

 few in the colony, and occurring only at certain times of the year; each 

 gonangium contains a blastostyle which produces planulae; no free 

 medusae: about 15 genera and 135 American species. 



Key to the genera of Sertulariidae here described: 



Qi Hydrothecae in two rows. 

 &i Hj'drothecae exactly opposite each other. 



Ci Operculum ;n 2 pieces (Fig. 173, A) 1. Sertularia 



Ca Operculum in 1 piece (Fig. 173, B) 3. Diphasia 



6o Hydrothecae alternate or subalternate to each other. 

 Ci Hydrothecae stand out from the stem. 

 di Hydrotheca with toothed margin ; operculum of 3 or 4 pieces. 



2. Sertularella 

 (Zo Hydrotheca with smooth margin ; operculum of one piece. .4. Abietinaria 



Ca Hydrothecae closely pressed against the stem 5. Tiiuiaria 



(u Hydrothecae in (me row, the openings turning alternately to the right and 

 left G. Hydrallmania 



* See "American Ilydroids, Part II, The Scrtularidae," by C. C. Nutting, U. S. 

 Nat. Mus. Spec. Bull., No. 4, 1904. 



