HYALONEMA (HYALONEMA) PLACUNA. 
207 
Authors attach considerable systematic importance to the structure of the 
organs of attachment in the hyalonematids, and have established genera (Phero- 
nema, Poliopogon) for sponges in which this attachment is effected by a broad 
spicule-brush or a number of separate spicule-bundles, and not, as in Lopho- 
physema, etc., and the species of the genus Hyalonema, by a simple slender stalk. 
Under these circumstances, and in view of the fact that the genus Hyalonema 
is characterized by the possession of a single slender stalk-spicule bundle, it at 
first sight seemed advisable to consider the sponge above described not as belong- 
ing to Hyalonema, and either to place it in one of the old polycaule genera 
(Pheronema or Poliopogon), or to establish a new genus for it. Since it has a 
rudiment at least of a gastral cone, which excludes it from Pheronema or 
Poliopogon; since it is very similar in habit and spiculation to the forms C, 
D, and E of Hyalonema ( Hyalonema ) agassizi; and since it seems to me very 
doubtful whether the difference between a monocaule and polycaule attachment 
is, by itself, sufficient for generic distinction, I place it in the subgenus Hyalo- 
nema. 
The nearest ally to it is H. (H.) agassizi. From this it differs by the large 
macramphidiscs, the pinnies, and the mode of attachment. The large macram- 
phidiscs are considerably longer, their anchors relatively much broader, and the 
distal parts of their anchor-teeth more straight and divergent in the sponge above 
described than in H. (II.) agassizi. The distal rays of the pinules of the former 
are more conic than those of the latter, and not distally thickened as in II . (H.) 
agassizi, the terminal cone consequently being much more slender than in H. 
(H.) agassizi. These pinule-rays differ also in respect to their spinulation, their 
spines being more numerous in H. (H.) agassizi than in II. (H.) polycaulum. H. 
(H.) agassizi has a single stalk, H. (H.) polycaulum has several. These, and other 
minor differences, render it advisable to separate these sponges specifically. 
Hyalonema (Hyalonema) placuna, sp. nov. 
Plate 63, figs. 29-51; Plate 64, figs. 1-19; Plate 65, figs. 1-23; Plate 66, figs. 1-5. 
Two specimens of this species were trawled in the Central Tropical Pacific 
at Station 3684 (A.A. 17) on 10 September, 1899; 0° 50' N., 137° 54' W.; depth 
4504 m. (2463 f.) ; they grew on a bottom of light yellow-gray Globigerina ooze. 
In their outer appearance they to a certain extent resemble Placuna shells 
and to this resemblance the name refers. 
Although similar and doubtlessly referable to the same species, the two 
