106 THE VOYAGE OF H.M.S. CHALLENGEPv. 



In the fir.st place, sleiulor sword-shaped hcxacts occur in great numljers. In these 

 both the prolonged ray and the four rectangularly intersecting transversals are smooth, 

 and terminate in a truncated point, \Yhile the sixth ray opposite the former is thickened 

 in its middle portion, and beset with outwardly-directed prongs. I am inclined to 

 believe that these sword-shaped hexacts represent the hypodermalia of the dermal 

 skeleton, and that they bore on their distal ray those iioricomes which were found here 

 and there, though indeed very much scattered, and which are figured in a fragment in 

 PI. XII. tig. 7. This lioricome form is distinguished by the small number (three to five) 

 of the terminal claws, and by a peculiar median outward bending of each of the six 

 terminal rays borne by each principal. 



Four different forms of rosette also occur. In the first place, discohexasters in which 

 each principal bears four terminal rays, slightly bent in an S-like manner ; these 

 terminal rays increase in thickness towards the exterior, and bear terminally a large hemi- 

 spherical terminal plate, with small marginal teeth (PI. XII. fig. 2). In the second place, 

 discohexasters with four straight terminal rays, each of which bears on its unthickened 

 extremity a deep campanulate terminal disc whose margins are divided into parallel 

 pointed teeth (PL XIII. fig. 4); thirdly, discohexasters half the size of the above, in 

 which each of the principal rays bears a bundle of from twenty to thirty thin terminals 

 varying in length, and terminating in small four-pronged transverse discs (PI. XII. 

 fig. 6); and fourthly, graphiohexasters with a bundle of very fine somewhat diverging 

 rhaphides, which are borne on the discoid terminal expansion of each principal ray 

 (PI. XII. fig. 5). As somewhat loose parenchymalia, the scattered simple hexacts and 

 diacts with central intersection nodes are to be noted. 



The reference of this sponge to the Euplectellidse, and to a position somewhere in the 

 neighbourhood of Tiegeria, I base upon the character of the main skeletal framework, 

 and on the great abundance of sword-shaped fioricome- bearing hexacts, which doubtless 

 belong to the dermal skeleton. 



Perhaps the variety A of Oscar Schmidt's Rhahdodictyum delicattvm^ is identical 

 with my Dictyocalyx gracilis, as is suggested by the figure,' and the short but very 

 apposite description of the framework which Oscar Schmidt has given in the words : 

 " an airy wall arises from a thick pillar-like base." I would also have accepted 

 0. Schmidt's designation for this Hexactinellid, had the name selected by 0. Schmidt 

 appeared to me to be more suitable for his variety B, to which his description 

 (especially of a peculiar rosette) chiefly refers. This variety B is likewise included in 

 the Challenger material, and will be immediately descril)ed. 



' Spongien des Meerbusens von Mexico, p. 46. - Loc. cit., pi. vii. fig 3r(. 



