27 



size and variation as those of H. alcoeJci, described above and illustrated in figs. 

 11-16, plate VI, are abundant near the surface. The great variability of these 

 paradises which I consider to be phylogenetically derived from ordinary amphi- 

 discs by the atrophy of one-half of each terminal disc, is truly remarkable. 



I was much surprised at the total absence of the micro-oxyhexactines with 

 strongly-curved rays, so abundant in Hyahnfma alcocJd. The most careful search 

 only brought to light a few oxyhexactines, the straight rays of which bear fine 

 and short, obliquely-situated spines, which point upwards. H. investigatoris 

 accordingly belongs to that group of Hyalonemas in which only very few micro- 

 hexactines, or none at all, occur in the parenchyme. 



The only specimen of HyaJonema investigatoris was found in the Bay of 

 Bengal 12° 20' N., 35' 8' E. in a depth of 3300 m.=1803 fths. 



Hyalonema afp-ne W. Marshall. 

 . Plate VII. 



I860 M. Schnltze Die Hyalonemen 4. p. 9. 



1875 Hyalonema affine W. Marshall in Zeitsclir. wiss. Znol. Bd. XXV Snjipl. p. 22i. 



1887 Hyalonema stylocalyx apertus F. B. Sch. in Abb. Prenss. Ak. 1886 p. 59. 



1887 Hyalonema apertum F. E. Sch. in " Challenger " Report, Hexactigellida p. 214, pi. XXXVIl, XXXVIII. 



1895 Hyalonema apertum and Hyalonema maehrpnthali F. E. Sch. in Abb. Preuss. Ak. 1S94 pp. 39-44 Taf. VIII. 



1899 Hyalonema affine reticulatum P. E. Sch. in Sitzber. Ges. nntnrf. Freunde in Berlin 1899 pp. 112-129. 



Two species of the " Investigator " Hexactinellida belong to the group of 

 Hyalonemas characterised by the presence of parenchymal microhexactines with 

 curved and spined rays. One of them is represented by a fuUgrown specimen 

 which, although possessed of a few insignificant peculiarities, can be assigned to 

 the species first described by Marshall in 1875 in the Zeitschrift fiir wissenschaft- 

 liche Zoologie (Bd. XXV, Suppl. p. 224) as Hyalonema affine, and later in 1887 

 by me in the " Challenger " Report as Hyalonema apertum F. B. Sch. from the 

 Sagami Bay (Japan). ■ 



The body of the sponge is caliculate or trumpet-shaped, 9 cm. long. At the 

 upper end, where the margin of the osculum bulges outward, the sponge is 5 cm. 

 broad. The central part of the body is slightly compressed and measures 2-3 

 cm. in transverse diameter. The lower end is conical and truncate (pi. VII, f. 

 1). The whole of the outer surface is uniformly covered with a quadratic dermal 

 reticulation. The inner surface of the wall surrounding the funnel-shaped 

 gastral cavity is even, smooth, and perforated by circular apertures of various size, 

 up to 4 mm. in diameter, which are distributed irregularly. There are typically 

 four, equal main excurrent openings, arranged crosswise. In the " Investi- 

 gator " specimen these have become very unequal : two of them lie side by side, 

 are very much enlarged and separated from each other by a very narrow space 

 only ; the other two are quite rudimentary. The free terminal part of the conus 



