THE SPONGES. 25 



(Figs. 1 and 5, Plate 2) the shaft is smooth and only slightly thickened at 

 the middle. The rays, 8 in number, are wide, tongue-shaped, rounded 

 at the free end, and closely approach the equator of the spicule, rays 

 of opposite umbels alternating. There is a depression at each pole of 

 the spicule. The precise shape of the umbel varies. In many spicules 

 (Fig. 5, Plate 2) it has an evenly rounded outline, while in others (Fig. 1, 

 Plate 2) it is truncated at tlie pole and flattened on the sides. The two 

 varieties shade into each other. A typical spicule with eveuly rounded 

 umbel has the following measurements: total length, 188 /a; depth of 

 umbel, 80 /a ; greatest width of umbel, 128 /u. ; shaft, 18 /^ thick at the 

 middle. A typical spicule with truncated and flattened umbel has the 

 following measurements: total length, 210 fi ; depth of umbel, 95 /x ; 

 greatest width of umbel, 152 /x ; shaft, 20 yx thick at the middle. 



Mesamphidiscs (Fig. 7, Plate 2), 60-80 ^ long, are present, but in 

 small number, in the parenchyma. The shaft bears scattered, minute, 

 sharp denticulations, and often but not always a circle of somewhat larger 

 similar protuberances at the middle. The umbels are deep bell-shaped, 

 slightly deeper than wide, and a little more than ^ the total length. The 

 umbel rays are 8 in number, rather narrow, and with pointed free end. A 

 typical spicule measures : total length, SO ft ; umbel depth, 36 jx ; umbel 

 width, 30 /x. 



Smaller amphidiscs, micramphidiscs, agreeing in shape with the mesam- 

 phidiscs, are scantily present. They range down to a total length of 28 /x. 



Hyalonema, species diversae. 



Plate 3, Figs. 12-16. 



Under this heading I briefly describe several specimens so fragmentary 

 that the shape of body cannot be inferred with any approach to certainty. 

 The skeletal elements of them all, especially of the forms designated 

 Ht/alonema 1 and Hijalonema ^, offer close resemblances to those of H. 

 bianchoraium. 



Hyalonema 1. 



Station 3381, a fragment, apparently from the lower end of the sponge, 

 including a part of the bundle of root spicules and surrounding tissue. The 

 bundle of root spicules in its thickest part has a diameter of 5 mm., and 

 the larger spicules a diameter of 700 ^. 



