REPORT ON THE SIPHONOPHOR^E. 41 



Family I. Discalidse, Haeckel, 1 



Discalidx, Hkl., System der Siphonoplioren, p. 29. 



Definition. — Disconectse with an octoraclial circular permanent umbrella, including 

 a circular, campanulate or cliscoidal pneumatocyst, without vertical crest. No vertical 

 sail upon the umbrella. Submarginal tentacles of the umbrella simple or branched, with 

 terminal cnidospheres. Central siphon surrounded by numerous mouthless palpons, 

 which bear the medusiform gonophores. 



The family Discalidse comprises some new, small, but very interesting Siphonophoraj 

 from the deep sea, which were found in the collections of the Challenger. They are in 

 general very similar to young Porpitidae, but differ from them in the very important 

 character, that the large central siphon alone possesses a mouth, while the surrounding 

 gonostyles or blastostyles are mouthless palpons. The Discalidse are therefore " Disco- 

 nectie monogastrica}," and become mature in the monogastric state, which is a transi- 

 tional larval stage in the Porpitidse. These latter, as well as the Velellidse, are in the 

 adult state " Disconectse polygastricse" each gonostyle possessing a mouth and repre- 

 senting a peripheral sexual siphon. The Discalidse may be regarded as the simplest and 

 most primitive of all Siphonophorse, since they retain the original character of a simple 

 octoradial Medusa (like Trachynema or Pectyllis) more nearly than all the others. 



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

 or discoidal, at other times more campanulate or even subglobular. The vertical or main 

 axis is, therefore, sometimes nearly as great as the horizontal or equatorial axis, at other 

 times scarcely half as great, or even less. The free prominent margin, or the glanduli- 

 ferous limbus umbrellse, marks the boundary between its upper (apical or proximal) face, 

 the exumbrella, and its lower (basal or distal) face, the subumbrella. The former includes 

 the pneumatophore, and represents with it the nectosome ; the latter is the siphosonw, 

 and bears in its centre the large primary sterile siphon, around this numerous sexual 

 palpons (or gonostyles), and towards the margin the corona of tentacles. 



A vertical meridional section through the umbrella (PI. XLIX. fig. 4) demonstrates 

 that the superior half of the umbrella is occupied by the pneumatocyst (ph), the inferior 

 by the large centradenia (uc), and from this depend in the centre the large central siphon 

 (sa), and around it the corona of gonostyles (gs). A deep circular coronal groove 

 separates this latter from the corona of submarginal tentacles. 



Exumbrella. — The superior (apical or proximal) face of the umbrella is flat or slightly 

 convex, smooth, and pierced by the stigmata of the pneumatocyst. It is composed of 

 two parallel lamellse, which are separated by the network of the pallia! vessels. The 

 external or superior lamella is the pneumatocodon, which contains numerous cnido- 



(ZOOL. CHALL. EXP. — PART LXXVII. — 1888.) Hllhh 6 



