EEPOET ON THE SIPHONOPHOE^. 51 



The structure of the cylindrical tentacles is the same as in all Porpitidae. They bear 

 three rows of pecliculate cnidospheres in their club-shaped distal half, one inferior and two 

 opposite lateral rows (figs. 4-6). 



Family II. Poepiiid^;, Brandt, 1835. 

 Porpitidx, Brandt, Prodromus, 25, p. 40. 



Definition. — Disconectae with a circular permanent umbrella, including a campanu- 

 late or discoidal pneumatocyst, which is composed of an octoradial centre and numerous 

 concentric rings, without vertical crest. No vertical sail upon the umbrella. Submarginal 

 tentacles with three rows of pediculate cnidospheres. Central siphon surrounded by 

 numerous peripheral fertile siphons, which bear the gonophores. 



The family Porpitidae, founded in 1835 by Brandt for the genus Porpita, comprises 

 all those Disconectae polygastricse which have a circular umbrella and a regular 

 originally octoradial ground-form. They agree in their regular octoradiate form with 

 the monogastric Discalidae, their ancestral group, but differ from them essentially in the 

 polygastric structure which they share with the Velellidae. Not only does the primary 

 sterile central siphon possess a mouth opening at its distal end, but likewise also each of 

 the surrounding gonostyles. These peripheral polypites, which bear the gonophores 

 budding from their proximal part, are therefore not mouthless palpons (as in the 

 Discalidae), but mouth-bearing, feeding, and digesting secondary siphons. The Velel- 

 lidae, with the same polygastric organisation, differ from the Porpitidae in the amphi- 

 thect or bilaterally-radial type, and in the development of a vertical sail upon the 

 exumbrella. 



Eschscholtz, in his fundamental work, 1 described five different species of Porpitidae, 

 which he united in the single genus Porpita. Lesson 2 added to this two other genera 

 (each with a single species), Ratis and Acies. His description, however, is very incom- 

 plete, and not illustrated by any figure, so that it is impossible to decide whether they 

 are merely young forms of Porpita (as most authors suggest) or perhaps Discalidse. 



Some interesting new Porpitidae, found in the Challenger collection, and some other 

 new forms observed by myself on different occasions, have led me to divide this family 

 into four genera (characterised in my System). 3 These may again be disposed in two 

 subfamilies, the Porpalidae and the Porpitellidae, each with two genera. The first 

 subfamily, Porpalidae, has a lenticular or subglobular umbrella and a campanulate 

 pneumatophore with lobate margin (Porpalia and Porpema) ; whilst the second sub- 

 family, Porpitellidae, possesses a flat discoidal umbrella and a medal-shaped pneumato- 

 phore with a circular, not lobate margin (Porpitella and Porpita). 



Umbrella, — The complete body of all Porpitidae is circular, sometimes more lenticular 



1 1, 1829, p. 176. 2 3, 1813, p. 592. 3 95, 1888, p. 30. 



