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



Although I ha\'e no specimens of this genus Ilahrodictyum for special examination, it 

 follows from Wyville Thomson's above quoted (p. 101) generic diagnosis and figures ' that 

 the two species distinguished by Wyville Thomson, Habrodictyum corbicida, Valenciennes, 

 and Habrodictyum speciosum, Quoy and Gaimard, are very closely related to Regadrella 

 phasnix, Oscar Schmidt. Whether the agreement goes so far that the two species must 

 be included in a common group I cannot decide, though I regard this as by no means 

 improbable. Wyville Thomson was certainly right in uniting Gray's two genera 

 Heterotella and Corbitella, and in entirely dropping the generic name Alcyoncellum , 

 which really referred to a calcareous sponge. 



Habrodictyum agrees with Regadrella in this, that the skeletal framework of the 

 tube-wall is formed of an irregular network of fibrous bundles, which in the upper part 

 are only united by means of the soft parts of the body, but which towards the somewhat 

 diminished inferior extremity become gradually more and more firmly welded together 

 by siliceous matter, and finally pass into a knotted base which grows directly upon the 

 solid substratum. The irregular distribution of the parietal apertures is characteristic of 

 both genera. The spicules described and in part figured by Wyville Thomson do not, 

 on the whole, differ much from the spicules of Regadrella. Only the rosettes, which are 

 scattered throughout the parenchyma, and which m Regadrella are provided with a trans- 

 verse terminal cross belonging to the terminal rays, exhibit in Habrodictyum speciosum 

 true oxyhexasters with proportionately long principal rays and shorter pointed terminals. 



While in Habrodictyum corbiculct the wall of the tube is affirmed to be sharply 

 separated from the transversely disposed terminal sieve-plate by a lip-like margin, such 

 a separation is entirely wanting in Habrodictyum speciosum, since the lattice-like net- 

 work of the tube-wall passes directly and without change into the gently arched terminal 

 plate. Whether Habrodictyum corbicida contains the parenchymal oxyhexasters which 

 are so abundantly present in Habrodictyum speciosum, has not been determined with 

 certainty. 



Genus 2. Eudictyum, Marshall. 

 This somewhat doubtful genus contains only a single species, Eudictyum elegans. 



Eudictyum elegans, Marshall. 



In his investigations into the Hexactinellida ^ Marshall has described, under the 

 name Eudictyum elegans, a specimen in the Museum of the Amsterdam Zoological 

 Garden, which is perhaps identical -^-ith the above-mentioned Habrodictyum speciosum 

 of Wyville Thomson, and at any rate, very closely allied to it. According to Marshall 

 the tissue of the wall of the hollow club-shaped sponge shows longitudinal and trans- 



• Ann. and Mag. Nat. Hist, ser. 4, vol. i. pi. iv. ^ Zeitschr.f. wi^s. Zool, Bd. xxv. p. 211, 1875. 



