302 HYALONEMA (PRIONEMA) FIMBRIATUM. 



The part, of the curve between 304.49 and 490.38 m pertains to the large 

 amphidiscs with smooth, divergent anchor-teeth, A; the part between 34.00 and 

 334.93 n to the amphidiscs with fimbriate, convergent anchor-teeth, B; and the 

 part between 14.42 and 41.14 /x to the amphidiscs with smooth anchor-teeth with 

 parallel end-parts, C. There is no dimensional overlapping of A and B and only 

 a slight overlapping of B and C, 14.42 and 34.00. The dimensionally transitional 

 forms of B and C causing this overlapping are, however, rare, so that the part 

 of the curve between 14.42 and 34.00 pertaining to them lies quite low. The 

 three differently shaped amphidisc-forms (A, B, and C) are differentiated accord- 

 ingly not only in regard to their shape but also in regard to their size (length). 

 Fig. 15 fxirther very clearly shows that the amphidiscs A and C vary 

 only slightly in size and form biometrically homogeneous groups, and that the 

 amphidisc B has a very wide range of dimensional variation and does not 

 form a biometrically homogeneous group. The part of the frequency-curve 

 pertaining to this group exhibits one high and rather broad and three smaller 

 elevations. This shows that the main-group B consists of four secondary groups, 

 the amphidiscs belonging to one of which are frequent, those belonging to the 

 three others, rare. It is therefore advisable to distinguish six groups (three 

 main-groups, one of which, B, comprises four secondary groups) of amphidiscs 

 in the sponges here described : — A, macramphidiscs, Ba, largest fimbriate 

 amphidiscs, Bb, large fimbriate amphidiscs. Be, small fimbriate amphidiscs, 

 Bd, smallest fimbriate amphidiscs, and C, micramphidiscs. 



The macramphidiscs (Plate 59, figs. 1-6; Plate 62, fig. 31) are 335-;446 /i long, 

 most frequently about 400 ijl. The shaft is cylindrical, straight, 8-16 n thick, 

 most frequently about 12 yu, and abruptly thickened in or near the middle to a 

 central tyle 11-22 /x in transverse diameter. The proportion of the thickness 

 of the adjacent parts of the shaft to the thickness of the tyle is 100 to 121-167. 

 From the tyle a verticillate bunch of spines arises. The number of the spines 

 forming this bunch is variable. Sometimes they are few in number and small 

 in size (Plate 59, fig. 2), sometimes numerous and large (Plate 59, fig. 1). Forms 

 intermediate between these extremes are the most frequent. The spines form- 

 ing these bunches are irregularly distributed and, when few in number, fre- 

 quently confined to one side of the shaft. The individual spines are 7-26 n 

 long, 4-5.5 M thick at the base, cylindrical throughout and terminally rounded, 

 or attenuated distally, truncate, and, provided with a cluster of exceedingly 

 minute secondary spinelets on the terminal face.' The primary spines arise 

 vertically or steeply from the central thickening of the shaft and are, farther on. 



