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



described in the following year (1880), as having been dredged at St. Lucia in 42.3 

 fathoms, and at Granada in 416 fathoms, and which he named Euplectella jovin. This 

 species is closely allied to Wyville Thomson's Euplectella siiberea, but differs from it in 

 its large prickles, which project freely outwards, and which, to the number of four or five, 

 form a ring round each of the circular parietal pores. It differs further in the possession 

 of a remarkable spicule with a fibula-like double hook. 0. Schmidt also describes a 

 transversely expanded inferior sieve-plate at the lower end of the tube, which differs 

 from the superior terminal plate only in being less firm. 



To the Euplectellidse 0. Schmidt also refers his Rcgadrella phoenix, Hertwigia 

 falcifera, and Rhabdopectella tintinnus. In all three the inferior extremity does not, 

 as in the genus Euplectella, run out into a basal tuft, but presents a tolerably firm basal 

 portion, which either consists, as in Regadrella, of a dense mass growing out into knobs 

 and lobes, or, as in Hertivigia, of irregularly branched protuberances, or finally, as in 

 Rhabdopectella, of a simple stalk with a disc-like terminal plate, which is frilled at the 

 margin. 



While the siliceous spicules of Regadrella phoenix do not differ essentially in form 

 from those of Euplectella asperg ilium, the general shape and the entire architecture of 

 the sponge is quite distinct. From the massive base a cup arises which is composed at 

 first of a much perforated plate, and further upwards of a flexible lattice-like network of 

 obliquely intersecting beams with round meshes. On the irregularly shaped uj)per 

 margin of the cup a spicular wreath projects like a cuff. The terminal aperture is, as in 

 Euplectella, closed by a sieve-plate. It is remarkable that within the cup of older dead 

 specimens younger forms had settled, so that two, or sometimes even three, individuals 

 appeared as if fixed into one another. 



On the branched basis of Hertivigia fcdcifera is seated an " irregular labyrinth of 

 cavities with thin membranous walls, which are supported by lattice-like plates of 

 obliquely crossed rods and fibres." On account of the deficient preservation of the 

 obviously very brittle upper portion, Oscar Schmidt was not able to ol^tain any definite 

 idea of the form of the entire sponge. Among the siliceous spicules which lie scattered 

 in the soft parts, there are, besides six- to three-rayed spicules and the typical Euplectella 

 floricomes, remarkable hexradiate rosettes with four-toothed terminal umbels attached 

 to the individual arms of the rays, and also rosettes with long backwardly bent teeth on 

 the terminal umbels, and especially the structures called by 0. Schmidt " sickle rosettes," 

 in which each of the six principal rays bears either four simple sickle-like teeth, or a 

 hemispherical terminal disc with several whorls of sickle-like teeth. Eods occur here and 

 there with numerous oblique lateral prongs at one end. 0. Schmidt mentions also, 

 delicate siliceous nets on whose exceedingly fine filaments small terminal hooks and 

 terminal umbels are found, but these nets seem to me to be fragments of Eadiolaria. 



The stalk of Rhabdopectella tintinnus, in older specimens, expands towards its upper 



