8 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



as long, sometimes longer, the distal edge convex and broadly rounded off at the 

 inner, abruptly rounded at the outer corners, in general parallel to the distal edge 

 of the interarticular ligament fossa, which forms the proximal edge of the mus- 

 cular fossa. The whole distal edge is convex, but less so toward the outer border. 

 The highest point is usually at about one-third of the distance from the inner to 

 the outer edge, from which point the height gradually decreases outwardly. The 

 internal gap between the muscular fossae is only about half as large as that between 

 the interarticular ligament fossae. 



Ventrally the space between the radials is filled with a spongy calcareous filling, 

 almost flat, reaching to about the height of the middle of the muscular fossae. The 

 central canal through this spongy calcareous mass is very small. 



Diameter of radial pentagon at base, 4.1 mm. ; height of articular face, 2 mm. ; 

 width, at transverse ridge, 2 mm. ; distance from center of rosette to middle of 

 dorsal outer edge of radial, 1.3 mm.; distance from center of ventral face of radial 

 pentagon to middle of ventral outer edge of radial, 1 mm. ; to angle between ra- 

 dials, 1.6 mm. 



CAl'ILLASTER SENTOSA. 

 Figs. 5, 6, p. C. 



The dorsal ligament fossa is between three and one-half and four times as 

 broad as high, with the proximal edge evenly and gently convex and the lateral 

 edges truncated and sharply rounded. The ligament pit is reniform, and much 

 larger than the transversely oval central canal. 



The transverse ridges of adjacent articular faces are in apposition, but the 

 dorsal ligament fossaj are entirely separated from each other. 



The outer edges of the interarticular ligament fossae have a general slight 

 inward slope. They are nearly straight, but curve outward both at the base and 

 distally. The distal edge is straight, or very slightly convex ; the outer distal angle 

 is sharply, the inner broadly, rounded; the inner edges form an S-shaped curve, 

 coming together just over the central canal, from which they are separated by a 

 narrow septum with parallel sides. The intermuscular furrow just over the central 

 canal is nearly as wide as the interarticular ligament fossae at the same level, but it 

 becomes constricted distally so that between the distal inner angles of the interartic- 

 ular ligament fossa? it is only about two-thirds of the proximal width. 



The muscular fossaj are narrow, about as broad as the transverse (greater) 

 diameter of the central canal. The distal outer edges are approximately parallel 

 to those of the interarticular ligament fossre ; but the muscular fossae may be slightly 

 broader exteriorly than interiorly. The distal outer angles project considerably 

 beyond the lateral edge of the interarticular ligament fosses. The distal outer angles 

 are sharply rounded ; the distal inner angles are broadly rounded, the inner edges 

 curving downward to the distal inner angles of the interarticular ligament fossae. 



The ventral surface of the radial pentagon is more or less obscured by a loose 

 calcareous deposit, which in the center forms a broad plug; its surface is radially 

 striate. 



