DESCRIPTION OF THE FAMILIES, GENERA, AND SPECIES. 



SIPHONOPHOR^E. 



Definition of the Class. — The Siphonophorse are swimming colonies or corms of 

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

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

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

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

 (Disconectae) ; the Siphonanthse comprise four orders — Calyconeetse, Physonectse, Auro- 

 nectas, Cystonectae. 



Synopsis of the Five Orders of Siphonophorse. 



I. DISCONANTFLE : Truncus or coenosome 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), . 1. Disconect.e. 



II. SIPHONANTH.E. 



Truncus or coenosome 

 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, 



2. Calyconect.e. 



A monothalam- 

 ous pneumato- 

 cyst or a float 

 filled with air is 

 always present. 



AVith nectophores 

 or with bracts 

 (often both to- 

 gether present). 

 With palpons. 



Without aurophore ; 

 common stem thin, 

 tubular, with a 

 simple canal, 



With an aurophore ; 

 common stem thick, 

 bulbous, with a net- 

 work of canals, 



3. Physojstectj;. 



4. AUEONECT.E. 



Without nectophores, and without bracts. 



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



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



Hhhh 4 



