322 HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 



18-90 IX long. It is to be noted that the macramphidiscs are much more numer- 

 ous in a than in b, while the micrampliidiscs are much more numerous in b than 

 in a. In consequence of this the number of macr- and micramphidiscs measured 

 and plotted in the figure are very different in the two specimens, and the sum- 

 mits of the two main elevations of the a- and 6-curve are very different in height. 



The larger (longer) macramphidiscs differ from the smaller (shorter) ones 

 morphologically by having relatively shorter anchors. The length frequency- 

 curves of the macramphidiscs show that these spicules by no means represent 

 a biometrically homogeneous group in respect to their length. The parts of 

 the macramphidisc curves below (to the left of) the above mentioned gaps 

 between 200 and 220 /.i in a and between 187 and 212 ^ in b are very regular 

 and obviously pertain to biometrically homogeneous groups ; the parts of these 

 curves above (to the right of) the gaps are on the other hand very irregular ' 

 and in no way in harmony with the others below (to the left) of them. I there- 

 fore think that the group macramphidiscs should lie subdivided into two 

 secondary groups: — large macramphidiscs with relatively short anchors, in 

 both specimens together 212-492 jj. long; and small macramphidiscs with 

 relatively long anchors, in both specimens together 1 10-200 /x long. 



The length frequency-curves of the micramphidiscs of both specimens 

 exhibit, besides the single main elevation, a number of small elevations. Most 

 of these are, as in the case of the large macramphidiscs, probably due to the 

 scarcity of the micramphidiscs of these sizes, which made it impossible to meas- 

 ure a larger number of them. Some of these elevations (two in the a-curve; 

 and one in the 6-curve, corresponding to one of the former) pertaining to the 

 largest micramphidiscs are, however, separated from the rest of the micramphi- 

 disc curves by very conspicuous gaps (between 54 and 79 ^ in the a- and between 

 ()6 and 79 yu in the 6-curvc). I therefore think it well to divide the micramphi- 

 discs according to these gaps into two subgroups: — large micramphidiscs, in 

 both specimens together 79-90 n long; and small micramphidiscs, in both speci- 

 mens together 18-66 ju long. 



The chief dimensions of the large macramphidiscs (Plate 85, figs. 1-7) are 

 tabulated on page 323. 



In these amphidiscs the shaft is straight and usually centrotyle. It is 



.either quite smooth (Plate 85, fig. 7) or bears a few low rounded knobs (Plate 



85, figs. 2, 4-6), sometimes also a single, straight, cylindrical, terminally rounded 



spine (Plate 85, fig. 1 ), which arises from its centre (central tyle). Occasionally 



' These irregularities are partly at least probably due to the rarity of these spicules, which made it 

 impossible to measure a larger number of them. 



