HYALONEMA (HYALONEMA) PLACUNA. 207 



Authors attach considerable systematic importance to the structure of the 

 organs of attachment in the hyalonematids, and have estabhshed genera (Phero- 

 nema, PoUopogon) 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 Pohopogon), 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 

 PoUopogon; since it is very .similar in habit and spiculation to the forms C, 

 D, and E of Hyalonema {Hyalonetna) 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 Hj^alo- 

 nema. 



The nearest ally to it is H. {H.) agassizi. From this it differs by the large 

 macrampliidiscs, the pinules, 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 di\'ergent in the sponge above 

 described than in H. {H.} agassizi. The distal rays of the pinules of the former 

 are more conic than those of the latter, and not distally thickened as in H. (H.) 

 agassizi, the terminal cone conseciuently 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 H. (H.) polycaulum. 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 re.semble Placuna shells 

 and to this resemblance the name refers. 



Although similar and doubtles.sly referable to the same species, the two 



