282 HYALONEMA (PRIONEMA) CRASSUM. 



I designate the four groups of amphidiscs: — ^ smooth macramphidiscs (group 

 1); serrated macramphidiscs (group 2); large micramphidiscs (group 3); and 

 small micramphidiscs (group 4) . 



The smooth macramphidiscs (Plate 108, figs. 14-17) are 290-370 n long, most 

 frequently about 337 ix. Their length frequency-curve is narrow and simple, 

 and has a single summit. The shaft of these spicules is straight, cylindrical, 

 18-30 At thick, usually 20-26 n, and thickened at or near the middle of its length 

 to a central tyle 4-12 /z more in transverse diameter than its adjacent parts. 

 Several broad, terminally rounded spines 3-8 m long arise from the central 

 tyle. The remaining parts of the shaft are smooth. 



The terminal anchors are 55-78 m in length, usually one sixth to one fourth 

 of the whole spicule, and 105-140 n broad. The proportion of their length to 

 their breadth is 100 to 155-236, on an average 100 : 174.3. The individual 

 teeth attain their maximum breadth of 20-30 ju in their distal part, and are very 

 abruptly pointed, the contour of their end-part having, when seen en face, the 

 shape of a broad gothic arch. The teeth are uniformly curved; the outer con- 

 tour of the anchor when seen in profile is generally nearly semicircular. 



The serrated macramphidiscs (Plate 107, figs. 1-5, 17-20) are 150-328 n long. 

 Their length frequency-curve is rather broad and irregular, and has three distinct 

 summits. The middle one is quite insignificant; the other two, situated at about 

 164 and 240 m respectively, are very pronounced. The shaft of these amphi- 

 discs is straight, 3-6 n thick, and thickened at or near the middle of its length 

 to a central tyle 2-6 m more in transverse diameter than its adjacent parts. 

 The central tyle bears a verticil of cylindrical, terminally rounded, straight or 

 curved spines 5-14 n long. The remaining parts of the shaft are covered with 

 numerous low protuberances (very short spines). 



The terminal anchors are 61-105 ^ long, the whole spicule being 2.5 to 3.5 

 times as long as the anchor. The maximum anchor-breadth is 45-100 fx. The 

 end-parts of the teeth of some of these anchors are nearly parallel ; in these anch- 

 ors the end-breadth is equal to the maximum breadth; the end-parts of the 

 teeth of others are convergent, — in these anchors the end-breadth is 2-6 m less 

 than the maximum breadth. The proportion of anchor-length to anchor-breadth 

 is 100 to 72-102, on an average 100 : 83.6. 



The individual teeth arise vertically from the shaft, are strongly bent in 

 their basal part, and straight or only slightly curved in their distal part. Their 

 tips are, as mentioned above, parallel or slightly convergent. The teeth attain 

 their maximum breadth of 12-15 ^ in their middle-part, and are attenuated 



