HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 311 



The polyps lie in excavations of the sponge-body just large enough for them. 

 Their distal ends are flush with the surface of the sponge. In life, when 

 expanded, they probably protruded more or less beyond its surface. These 

 polyps form groups within which they are about 4.5 mm. apart (Plate 83, fig. 

 60). The coenenchym-like mantle enclosing the upper end of the stalk, which 

 has been referred to above, may have formed part of a colony of polyps similar 

 to those in the body of the sponge. Some of the polyps in the sponge-body which 

 I examined bore a short thread-like protuberance on their lower (inner) end. 

 Probably all the polyps of a group, possibly all the polyps of the whole sponge, 

 are connected by such threads. I did not make sure of this, however, because 

 for this purpose it would have been necessary to cut up the fine and unique 

 specimen. 



The pinules (Plate 82, figs. 21-34; Plate 83, fig. 45b). The dermal pinules 

 of the upper and middle-parts of the body in both specimens resemble, as radial 

 sections show, the gastral pinules, but differ from the dermal pinules on the 

 basal part of the sponge, the latter being larger and having distal rays with more 

 divergent spines. In the spicule-preparations of different parts of the surface 

 besides the pinules shown by the sections to be truly proper to the region in 

 question, I always found a few others; in the spicule-preparations of the gastral 

 membrane and the upper and middle -parts of the dermal membrane were typi- 

 cally basal spicules; and in the spicule-preparations of the basal part of the 

 dermal membrane were pinules of the type found in situ on the upper parts 

 of the sponge. 



The principal dimensions of the pinules are tabulated on p. 312. 



The gastral pinules (Plate 82, figs. 29, 30; Plate 83, fig. 45b) and the dermal 

 pinules on the upper and middle-parts of the sponge (Plate 82, figs. 22, 31-33) are 

 nearly always pentactine, very rarely hexactine. Their distal ray is straight 

 and 120-280 ii ' long. It ends with a terminal cone free from spines. Its proxi- 

 mal part is also spineless, and it arises with a trumpet-shaped extension from the 

 cross formed by the lateral rays. Farther up the distal ray becomes thinner, 

 and it attains its minimum thickness at a distance of about 30 yu from its base 

 (the centrum of the spicule). Beyond that it again becomes thicker. At its 

 thinnest point the smooth proximal part of the distal ray is 7-11 /u thick. The 

 basal thickening is variable. The distal ray of a typical upper dermal pinule is 

 17 yu in diameter at its thickened base, 30 n higher up, and 11 fi at its thinnest 

 point. The whole of the distal ray, with the exception of its proximal and distal 



'This and the following measurements refer to the pinules of both specimens together. 



