HYALONEMA (PRIONEMA) FIMBRIATUM. 



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shaft, are strongly curved, concave to the shaft, for a short distance quite at the 

 base, and sHghtly and quite uniformly curved in the same direction for the 

 remainder of their length. The total curvature is such that the ends of the 

 teeth converge towards the shaft, and enclose with it angles of about 8°-16°. 

 The body of the tooth has the usual T-shaped transverse section. The lower 

 (radial) part increases in height proximally to 5-9 yu. The upper (paratangen- 

 tial) part is 6-10 y. broad near the middle of the length of the tooth and attenu- 

 ated both proximally and distally. The distal end of the body of the tooth is 

 narrow and blunt-pointed. 



The two margins of the outer part of the tooth (which corresponds to the 

 horizontal upper stroke of the T) are continued in fine, frill-hke, fimbriate, 

 siliceous membranes, which diverge from the plane through tooth- and shaft- 

 axis and extend obliquely inward. The tooth, together with its two fimbriate 

 marginal membranes, has a transverse section (Fig. 16). 



Upper (paratangential) part of the tooth. 



Marginal fimbriate membrane. 



Lower (radial) part of the tooth. 



Fig. 16. — Anchor-tooth. Section. 



The fimbriate marginal membranes extend from the base (Plate 61, figs. 

 4, 5, 8, 9) to the tip (Plate 61, figs. 6, 7, 10) of the tooth and even slightly beyond 

 it. They are at the base of the tooth quite narrow, only about 1 ij. broad (Plate 

 61, figs. 4, 5, 8, 9) ; in the middle of the tooth (Plate 61, figs. 1-3) they broaden 

 distally and attain a breadth of about 7 m- Beyond they again become slightly 

 narrower and are, at the end of the tooth, about 4 m broad. Narrow and deep 

 incisions, extending down to the body of the tooth, divide these membranes into 

 lobes, which are, in the distal and middle-part of the tooth, on an average about 



