9Q 

 MONOGRAPH OF THE EXISTING CKINOIDS. ^» 



The outer edges of the interarticular ligament fossse make an angle of 

 approximately 60^ with the transverse ridge and are slightly and uniformly 

 concave. The outer distal angles are very sharp, the distal borders of the fossa? 

 running inward and downward at an angle of about GO^ After reaching a 

 len-th equal to nearly or quite one-half that of the outer border the distal edges 

 turn abruptly downward and, after making a deep S-shaped curve, the two 

 ed-es join just above the central canal. This lower edge of the intermuscular 

 furrow is bowed upward, following the curvature of the central canal from 

 which it is separated by a very narrow isthmus. 



The muscular fossa are small, rounded triangular, with the apex at the 

 inner distal angle of the interarticular ligament fossse. Their distal edges are 

 convex the chord of the convexity being approximately parallel with the trans- 

 verse rido^e Their rather sharply rounded outer angles project somewhat beyond 

 the outer'distal angle of the interarticular ligament fossa>: their broadly rounded 

 inner an<^les are very widelv separated. The intermuscular furrow is shallow, but 

 very bro'ad; its lateral borders vary from parallel with the lateral borders of 

 the^nterarticular ligament fossfe to almost parallel with each other; as a rule 

 the condition is nearer the latter. At the level of the distal edge of tlie central 

 canal the width of the intermuscular furrow is about equal to the distance from 

 the end of the transverse ridge to a perpendicular from the transverse ridge to 

 the outer border of the furrow; distally the width of the furrow decreases, being 

 not much more than one-half as great between the inner angles of the muscular 



f 0SS8G 



The ventral surface of the radial pentagon is covered with a loose calcareous 

 deposit which reaches nearly to the height of the distal edges of the muscular 



Diameter of radial pentagon at base, 3.6 mm. ; height of articular face (meas- 

 ured along the inclination), 1.9 mm.; width, at transverse ridge. 1.9 mm.; dis- 

 tance from center of rosette to middle of dorsal outer edge of radial, 1.8 mm.; 

 distance from center of ventral face of radial pentagon to middle of ventral face 

 of radial, 0.8 mm. ; to apex of interradial angle, 1.1 mm. 



AMPHIMETRA ENSrFER. 

 Figs. 30 40, p. 26. 



The dorsal ligament fossa is deep, not quite twice as broad as high, evenly 

 curved proximally. The ligament pit is rounded reniform. about the size of the 



central canal. „ , , ,, i i i- 4. 



The ends of the transverse ridges just join laterally, but the dorsal hgament 

 fossa? are widely free, owing to the low angle at which their proximal borders 

 join the ends of the transverse ridges. ,^ i- , - 



The interarticular licament fossa" are about as high as the distance from 

 the central canal to the ends of the transverse ridge : their outer borders are slightly 

 concave and slope inward, making an angle of about 60^ with the transverse ridge; 



