270 HYALONEMA (PRIONEMA) AZUERONE. 



an angle of 10°-20°. The teeth have the usual T-shaped transverse section. 

 The lower, radial part, corresponding to the upright stroke of the T, extends 

 to the end of the tooth. The upper, paratangential part, corresponding to the 

 upper, horizontal stroke of the T, is 12-16 /j. broad in its middle-part and grad- 

 ually attenuated distally; its end is broad and simply rounded; its lateral 

 miirgins are strongly serrated (Plate 58, figs. 5-9). The individual saw-teeth 

 are pointed and usually triangular. In the middle-part of the anchor-tooth 

 these saw-teeth are 1-2 n long and close together. Distally they become smaller 

 and more distant; at the end they are only about 0.5 m long. The saw-teeth 

 are directed obliquely inward. A similar serration of the teeth was found 

 also in H. spinosum (p. 276) and in a few others. 



In a few of the macramphidiscs observed two or three supernumerary 

 shaft-rudiments arose from the central tyle. In one of them, two of these 

 rudiments bore somewhat reduced and irregular terminal anchors. 



The large mesamphidiscs (Plate 57, fig. 8) are very rare; the one represented 

 is 232 n long. Its shaft is 5.5 n thick and its central tyle 8 m- A verticil of spines, 

 with a maximum length of 4 fi, arises from the latter, and numerous short and 

 broad spines cover the remaining parts of the shaft. The terminal anchors are 

 semioval, 108 ^ long, and 72 ^ broad; the proportion of their length to their 

 breadth being 100:67. 



The medium mesamphidiscs (Plate 57, figs. 6, 7; Plate 58, figs. 2, 13) are 

 very numerous. They measure 56-130 jx in length, most frequently about 85 m- 

 Their shaft is 1.3-3 yu thick and abruptly thickened in or near the middle to a 

 central tyle 1.5-5 n in diameter. The proportion of the thickness of the shaft 

 to that of the tyle is 100 to 140-220, on an average 100 : 165.4. A verticillate 

 bunch of irregularly curved, obtuse spines 1-3.5 fi long arises from the tyle. 

 Similar, usually much shorter spines are scattered in greater or smaller numbers 

 irregularly over the remaining part of the shaft. The degree of spinulation of 

 the shaft is correlated with, and in proportion to, the size of the spicule; the larger 

 the amphidisc the larger and the more numerous the spines. The anchors are 

 15^6 fi long, one third to nearly half of the whole spicule, and 12.5-31 fj. broad. 

 The proportion of their length to their breadth is 100 to 57-83, on an average 

 100 : 68.6. This proportion is correlated to the size of the spicule, the anchors 

 being on the whole relatively the narrower, the larger the spicule (the anchor). 

 The average proportion of length to breadth of the anchors under 20 m in length 

 is 100 : 80.5, of the anchors under 30 n in length 100: 72.3, and of the anchors 

 over 40 m in length 100 : 65.9. The anchors usually consist of twelve or thirteen 



