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



Tentacles (figs. 1-4, t). — The eight tentacles are cylindrical, somewhat larger than the 

 diameter of the umbrella, and bear a single cnidosphere at the distal end. 



Genus 2. Disconalia, 1 Haeckel, 1888. 



Disconalia, Hkl., System der Siplionoplioren, p. 30. 



Definition. — Discalidse, with a lenticular or discoidal umbrella, including a discoidal 

 pneumatocyst, which is composed of a central chamber, eight surrounding radial chambers, 

 and several concentric ring-chambers. Marginal tentacles numerous, arranged in eight 

 radial bunches. 



The genus Disconalia is closely allied to the preceding ancestral genus Discalia ; but 

 it differs from it in the multiplication of the marginal tentacles, which form eight marginal 

 bunches ; and mainly in the peripheral increase of the octoradial pneumatocyst, which 

 is surrounded by several concentric ring-chambers. It corresponds therefore to that 

 larval stage of the Porpitidae which Alexander Agassiz 2 has figured of Porpita linnsena. 

 The young larvse, probably of all species of Porpitidse, after having passed the Discalia- 

 form, assume a transitional Disconalia-form. 



Perhaps even Eschscholtz observed a Disconecta belonging to this genus. The 

 interesting small form, taken in the tropical Pacific, which he figures under the name 

 Porpita ramifera, 3 is either a true Disconalia, or the corresponding larva of some 

 Porpitid passing through this typical stage. The answering of this question is not 

 possible, since the organs of the subumbrella, which would be decisive, are neither 

 figured nor even mentioned in the description given by Eschscholtz. 



Two species of Disconalia (both deep-sea inhabitants) were found by me in the 

 Challenger collection, one from the Southern Pacific (Station 181), the other from the 

 Indian Ocean, south of Australia (Station 157). The latter (Disconalia pectyllis) had 

 much longer and less ramified tentacles, and a larger pneumatocyst, than the former 

 (Disconalia gastroblasta) ; but its state of preservation was not sufficient for a full 

 description. Eegarded from a phylogenetic point of view, Disconalia is of the highest 

 importance as a necessary connecting link between Discalia and Porpalia. It is 

 derived from the ancestral genus Discalia by the multiplication of the air-chambers and 

 the tentacles ; if its gonostyles accprired a mouth, it would pass into Porpalia. 



Disconalia gastroblasta, n. sp. (PI. XLIX. figs. 7-12; PL L. figs. 1-10). 



Habitat. — Southern Pacific, north-east of Australia, Station 181, August 25, 1874 ; 

 lat. 13° 50' S., long. 151° 49' E. ; depth, 2440 fathoms. 



1 Disconalia, derivative from Discalia. - 57, pi. ix. tig. 3. 3 1, p. 17, Taf. 1C, figs. 3o, 36. 



