26 THE VOYAGE OF H.M.S. CHALLENGER. 



Subclass I. DISCONANTH^E. 



Order I. DISCONECT^, Haeckel, 1888. 

 (Pis. XLIII. to L.). 



CJiondmphorx, Chamisso, 1821, 16, 1 p. 363. 

 Velellidx, Eschscholtz, 1829, 1, p. 165. 

 Cirrhigradx, Blainville, 1834, 24, p. 303. 

 Porpitarix, Haeckel, 1869, MS. Canar. 



Definition. — Sipkonophorse with a permanent primary umbrella, without necto- 

 phores and bracts. Nectosome campanulate, lenticular or discoidal, including a poly- 

 thalamous, originally octoradial pneumatocyst, which exhibits numerous stigmata on its 

 upper face, and tracheae on its lower face. Siphosome composed of a central primary 

 siphon, and one or more concentric girdles of gonostyles (either secondary siphons, or 

 instead of these palpons), the latter producing gonophores. The primary larva 

 (Disconula) has a regular octoradial umbrella, with eight radial canals and a connecting 

 circular canal at the margin, which bears eight primary radial tentacles. 



The order Disconectae comprises three families, the Discalidae, Porpitidae, and 

 Velellidae ; all members of this order agree in so many important characters, and differ 

 so widely from all the other Siphonophorae, that I divide the whole class into two 

 subclasses, Disconanthae and Siphonanthae. The first subclass, Disconanthae, 

 represented by the Disconectae only, is developed from the octoradial and octonemal 

 medusoid larva Disconula ; it retains the primary corona of eight or more marginal 

 tentacles, possesses a centradenia, and produces the polymorphous persons by budding 

 from the subumbrella. The second subclass, Siphonanthse, on the other hand, represented 

 by four orders (Calyconectae, Physonectae, Auronectae, and Cystonectaa), differs in the 

 bilateral form of its mononemal larva, Siphonula ; this, as well as each of the following 

 siphons, has only a single tentacle ; the centradenia is wanting, and the polymorphous 

 persons of the cormus bud in the ventral line of the primary siphon. 



History.-— Eschscholtz, in his fundamental work, 2 separated from the other Siphon o- 

 phorae the family Velellidae, comprising the genera Porpita and Velella of Lamarck 

 (1815). So early as 1821 these were united as "Medusae chondrophorae " by Chamisso 

 and Eysenhardt. Eschscholtz added as a third genus Rataria, and found the peculiar 

 character of all Velellidae in the possession of an internal polythalamous cartilaginous 

 shell, the chambers of which are filled with air. Brandt afterwards (in 1835, 25) 

 separated the Porpitidae (with circular shell, without vertical crest) from the true Velellidae 



1 The figures in black type refer to the Bibliography at the end of the Report. 



2 System der Acalephen, 1829, p. 165, (1). 



