HYALONEMA (HYALONEMA) OBTUSUM. 171 



The small micramphidiscs of var. gracilis (Plate 35, fig. 17b; Plate 37, 

 figs. 1-5; Plate 38, figs. 1-3) are 13-26 ju long, most frequently about 16.7 ti. 

 The shaft is straight and 0.5-1.2 yu thick. It bears in its central part a few short 

 and broad, terminally rounded protuberances. The terminal anchors are 5-9 ix 

 in length, that is a third to two fifths of the whole spicule, and 4.2-8 m broad. 

 The proportion of the length to the breadth of the anchors is 100 to 55-120, on 

 an average 100 : 90. 



The small micramphidiscs of var. robusta (Plate 40, figs. 16-18, 20a) are 

 similar but somewhat smaller. Their measurements are: — length 12-23 n, 

 most frequently about 16.2 i^; anchor-length 3.8-7 ju, that is about a third of the 

 length of the whole spicule ; anchor-breadth 4-5 yu ; proportion of anchor-length 

 to anchor-breadth 100 to 72-125, on an average 100 : 90. 



A few young forms of micramphidiscs were observed in var. robusta. These 

 spicules (Plate 40, fig. 18) have a centrotyle and spiny shaft thickened at both 

 ends. Their anchors appear as terminal verticils of small vertically arising and 

 shghtly recurved teeth. 



The two specimens described are in respect to their spiculation similar 

 enough to be considered the same species. Their skeletal elements, however, 

 differ in detail, the spicules generally, and particularly both the stout and the 

 slender tetractine and tetractine-derivate acanthophores, having much stouter 

 rays. The uncinates are larger and the anchors of both kinds of macramphi- 

 discs and of the large micramphidiscs are relatively considerably broader in 

 the specimen from Station 3681 (A. A. 2) than in the specimen from Station 

 3684 (A. A. 17). For this reason and because the two specimens differ con- 

 siderably in outer appearance and come from localities a good distance (over 

 3000 km.) apart, I think it advisable to consider them as two distinct varieties. 



The only species of Hyalonema which appears to be at all closely allied to 

 these sponges is the one described in this report as Hyalonema (H.) agassizi. From 

 this they differ chiefly by their macramphidiscs and large micramphidiscs having 

 more strongly curved and less divergent teeth, by their microhexactines being 

 smaller and having more strongly curved rays, by the spicules of their acantho- 

 phores being larger, and by the rays of the slender acanthophores having longer 

 spines. 



