222 HYALONEMA (HYALONEMA) TENUIFUSUM. 



In respect to its large pinules this sponge somewhat resembles Hyalonevia 

 (Hyalonema) placuna, in respect to its large amphidiscs Hyalonema (Hyalonema) 

 polycaulum. 



Hyalonema (Hyalonema) tenuifusum, sp. nov. 

 Plate 67, figs. 1-20; Plate 68, figs. 1-25. 



A larger (a), and several fragments of another, smaller (b) specimen of this 

 sponge were trawled off the coast of northern Peru at Station 4656 on 13 No- 

 vember, 1904; 6° 54.6' S., 83° 34.3' W.; depth 4063 m. (2222 f.); it grew on a 

 bottom of fine, green mud mixed with gray ooze; the bottom-temperature 

 was 35.2°. The name refers to the minute, exceedingly slender, centrotyle 

 amphioxes so abundant in these sponges. 



Shape and size. Specimen (a) (Plate 67, fig. 1) appears as a somewhat 

 lacerated lamella, irregularly oval in outline, 84 mm. long, and 56 mm. broad. 

 At one of its narrower ends a stalk, 3 mm. thick, arises from its margin. This 

 stalk lies in the same plane as the lamellar body of the sponge. The latter 

 is stoutest some 20 mm. above the point where the stalk arises from it, and is 

 here 12 mm. thick. Upwards and sideways the lamella gradually thins out 

 towards the margin. The fragments of specimen (&) are lacerated pieces of a 

 lamella 1.5-3 mm. thick. The lamellar body is not simple and solid throughout, 

 in either of the specimens, but is partly composed of two lamellae in contact 

 with each other. The inner surfaces of these lamellae are obviously gastral 

 surfaces and it is probable therefore that these sponges are in truth calyculate, 

 and that their present shape is due merely to a collapse of the walls, caused by 

 pressure exerted during or after capture. 



The colour in spirit is brown, rather dark in (a), pale in (b). 



The skeleton. Both the outer dermal and the inner gastral surfaces are 

 covered by a dense pinule-fur. Smaller gastral pinules have been found in the 

 walls of some of the canals. Below the dermal and gastral surfaces masses of 

 paratangential rhabds form a kind of felt. These rhabds are mostly centro- 

 tyle amphioxes, but derivates of these spicules, with one actine reduced in length 

 and often thickened and terminally rounded, also occur among them. This 

 spicule-felt is pierced by the proximal rays of hypodermal and hypogastral 

 pentactines. Similar amphioxes and amphiox-derivates and occasionally hex- 

 actine megascleres were observed in the interior. The microscleres are regu- 

 lar microhexactines, irregular microhexactines with two opposite rays much 

 longer than the others, minute centrotyle amphioxes, minute tylostyles, large 



