DESCRIPTION OF THE FAMILIES, GENERA, AND SPECIES. 



SIPHONOPHORffi. 



Definition of the Class. — The Siphonophoras are swimming colonies or eorms of 

 Hydroniedusse, composed of polymorphous medusoid zooids or persons, which arise by 

 budding from an original simple Medusa. The class is divided into two subclasses : — the 

 Disconanth^e arise by budding from the subumbrella, the Siphonanth^e by budding 

 from the manubrium of the original Medusa. The Disconanthae comprise one order only 

 (Disconecta?) ; the Siphonanthse comprise four orders — Calyconectse, Physonectse, Auro- 

 nectae, Cystonectse. 



Synopsis of the Five Orders of Siphonophorse. 



I. DISCONAJNTILE : Truncus or ccenosome formed by the umbrella of the original 

 octoradial Medusa, which includes a polythalamous pneumatocyst ; the buds arise 

 in concentric girdles from the subumbrella. Larva octoradial (Disconula), 



II. SIPHONANTH.E. 



Truncus or ccenosome 

 formed by the manu- 

 brium of the original 

 bilateral Medusa ; the  

 buds arise in the ven- 

 tral line of the manu- 

 brium. Larva bilateral 

 (Siphonula). 



No pneumatocyst or float filled by air. No palpons. 

 Always one or more nectophores are present, 



A monothalam- 

 ous pneumato- 

 cyst or a float 

 filled with air is 

 always present. 



With nectophores 

 or with bracts 

 (often both to- 

 gether present). 

 With palpons. 



i 



1. Disconectj:. 



2. Calycoxect.e. 



Without aurophore ; 

 common stem thin, 

 tubular, with a 

 simple canal, 



With an aurophore ; 

 common stem thick, 

 bulbous, with a net- 

 work of canals, 



3. Physonectj:. 



4. AURONECT.E. 



Without nectophores, and without bracts. 



Pneumatocyst with an apical stigma, . 5. Cystonect.e. 



(ZOOL. CHALL. EXP. — PART LXXVII. — 1888.) 



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