8 



occur in greater or smaller numbers. These macro-uncinates are covered mth 

 spines situated very obliquely, and extending nearly parallel, closely " anliegend," 

 to the shaft of the spicule (pi. I, f. 13). They are arranged radially, the thicker 

 distal end lies in the outer surface of the sponge. 



The root-tuft is about as long as a hand. The basalia composing it are 

 arranged in bundles 3-5 mm. thick. The smooth, upper, gradually-pointed ends 

 of these spicules are imbedded in the sponge for a length of several centimeters. 

 Their much longer free part extends more or less vertically downward into 

 the silt on which the sponge grows. This part is not covered with conuli-like 

 shagreened tubercles, like the distal parts of the marginalia : it is either quite 

 smooth, or bears, as is the rule in basalia of Hyalonematidse, flattened spines 

 exteudmg obliquely upwards. All the basalia not broken off which I examined 

 terminated distally in the two-teethed anchors, characteristic of the genus 

 Plieronema. 200-300 m above the distal end the spines disappear and the shaft 

 is slightly attenuated. Towards the distal end it thickens, first gradually, then 

 abruptly, to form the central inflated part of the anchor which has a thick- 

 ness of 60 M. The two anchor-teeth are broad and flattened. Their distal contour 

 has the shape of a rounded gothic arch. The chord between the points of the 

 teeth is 600-800 m long. The sharp lateral edges of the teeth have a slightly 

 prominent bend in the middle. These edges are joined by two crests traversing 

 the shaft (pL I, f. 12). 



I will now describe the microscleres. Pinnies are met with in the dermal 

 and gastral membranes, where they generally stand close together, theii' basal 

 rays extending side by side for considerable lengths and forming a network 

 with quadratic meshes. On narrower strips of dermal membrane, between 

 pores, they form single rows and are further apart. The pinules are 70-140, 

 usually 80 m, high. The iowv basal rays are nearly always quite straight and form 

 a regular cross with beams intersecting vertically. They are on an average about 

 50 /* long and 6 ^ thick, proximally cylindrical and smooth, distally slightly in- 

 flated and covered with sparse, vertical, sharp tubercles. The distal inflation 

 tapers towards the basal and the terminal part of the ray (pi. I, f. 7, 8j. The 

 centre of the spicule is slightly thickened, but there is no trace of a sixth, 

 proximal ray. The distal ray is vertical to the plane of the four basal rays. It 

 consists of a smooth, cylindrical proximal part 9 M thick and 12 ^ or more long, 

 and a bushy distal, conical or carrot-shaped part covered with curved spines. 

 This distal part is 60-130, usually 70 m, long and 40 /* broad. Most of the pinules 

 have a short terminal spine and very numerous and dense, long and stout lateral 

 spines, terminally only slightly curved, extending obliquely upwards (pi. I, f. 8). 

 Some of the pinules however are longer and more slender, have a longer and 

 thinner terminal spine and less numerous but equally stout lateral spines which 

 are curved more strongly. The pinules of the terminal sieve-plate are on the 



