HYALONEMA (HYALONEMA) AGASSIZI. 191 



average 100 : 103. The anchor-teeth are T-shaped in transverse section. The 

 upper part appears as a curved band, for the greater part of its length 8.7-11.5 /u 

 broad, and attenuated to a point or, more rarely, rounded off at the end. The 

 teeth arise steeply and are uniformly curved, concave to the shaft. The curva- 

 ture is not very great and never suffices to give the end-parts of the teeth a 

 direction parallel to the shaft. The tangents on these end-parts enclose, in the 

 adult large amphidiscs, angles of about 5° with the axis of the shaft. In young 

 spicules of this kind (Plate 46, fig. 9) this angle is, of course, much greater. 



The large macramphidiscs of form B (Plate 46, fig. 15) are 126-310 ix long, 

 most frequently about 240 fi. Their shafts are 8-14 /z thick, and their anchors 

 are 46-67 // long and 48-76 m broad. These spicules are longer and have smaller 

 anchors than those of form A. 



The large macramphidiscs of form C (Plate 46, figs. 10, 11) are 110-290 n 

 long, most frequently about 240 /j. Their shafts are 6-10 m thick, and their 

 anchors 40-63 n long and 35-75 yu broad. They are very similar to those of 

 form B, and are like them longer and provided with smaller anchors than those 

 of form A. 



The large macramphidiscs of form D (Plate 46, figs. 6-8, 16) are mostly 

 regular and similar to those of the other forms. They are 132-282 ti long, most 

 frequently either about 240 or 180 m, with shafts 9.5-12 /i thick, and with anchors 

 52-73 n long and 48-66 n broad. In respect to their length the regular large 

 macramphidiscs of form D are intermediate between forms B and C on the one 

 hand and form A on the other. Their anchors are similar in size to those of 

 forms B and C. In the specimen of form D I found an irregular large macram- 

 phidisc (Plate 46, fig. 7) 192 ix long, with a shaft 4.4 n thick. The two anchors 

 of this spicule are both about 26 /x broad but very unequal in length, one being 

 44 n long, the other considerably shorter. The shaft is beset with numerous 

 large pointed spines, all strongly bent towards one end. These spines increase 

 in size towards the end from which ihey diverge; the largest is 16 ju long. 



The large macramphidiscs of form E are 150-280 yu long, u.sually 170-256 n, 

 most frequently about 200 ^u. Their shaft is 6-12 yu thick. Their anchors are 

 51-67 ti long and 51-80 ij. broad. 



The large macramphidiscs of form F are 112-260 /i long, usually 150-232 ix, 

 most frequently about 200 ti. Their anchors are 36-65 ix long and 34-70 tx 

 broad. In a preparation of one of the specimens of tliis form I found an ab- 

 normal large macramphidisc, in which the central spine- verticil was replaced 

 by an anchor similar to but slightly smaller than the terminal anchors. 



