44 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The muscular fossae are usually narrowly linear, but the distal edge may be 

 more or less strongly convex. They are in breadth equal to about one-half the 

 horizontal diameter of the central canal. The outer edge inwardly turns down- 

 ward, so that the short inner edges are parallel ; these run downward to the junction 

 of the distal edge of the interarticular ligament fossae and the rim about the central 

 canal, and are separated by a shallow rounded furrow of about their own width. 

 This furrow is usually carried back for a slight distance over the ventral side of 

 the radials. 



The muscular fosste lie in the same plane as the interarticular ligament fossse 

 and are always perfectly evident when the latter are viewed perpendicularly. They 

 do not, so far as I have seen, incline toward the horizontal so as to be with difficulty 

 recognizable in a direct view, as described by Carpenter. 



The ventral face of the more or less stellate radial pentagon is moderately 

 concave, with more or less of a deposit of loose calcareous matter, especially toward 

 the center. The ventral surface of the radials, where not concealed by a secondary 

 deposit, is radially striate. 



Diameter of radial pentagon at base, 5.5 mm. ; height of articular face 

 (measured along the inclination), 2 mm.; width, at transverse ridge, 2.6 mm.; 

 distance from center of rosette to middle of dorsal outer edge of radial, 2.7 mm. ; 

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

 edge of radial, 1 mm. ; to apex of interradial angle, 1.5 mm. 



PTILOMETRA MACKONEMA. 



Figs, n??., 974, ijI. 2. 



A8TEROMETRA MACROPODA. 

 Figs. 60, 70, p. 43. 



The portion of the radial articular face between the transverse ridge and the 

 distal end of the interarticular ligament fossa; lies in a plane making an angle of 

 only about 30° with the plane at right angles to the dorsoventral axis of the 

 animal, so that tliis portion of the radial articular face as a whole makes an angle 

 of about 120° when the radial pentagon is viewed from the side. The dorsal liga- 

 ment fossa lies in a plane which makes a slight angle with the plane of the other 

 joint face elements. The muscular fossa; stand up somewhat abruptly, inclining at 

 an angle of about 30° to the dorso^-entral axis and at an angle of about 60° to 

 each other. The dorsal ligament fossae are entirely separated from each other, but 

 the ends of the transverse ridges are in contact. The lateral borders of the inter- 

 articular ligament fossa; recede gradually from each other, forming between them a 

 narrow V-shaped interradial gap, but the outer edges of the muscular fossa^. 

 curving outward, meet and are in apposition for almost their entire length. 



The dorsal ligament fossae are about three times as broad as long, the proximal 

 border being regularly curved. 



The rim about the central canal is broad and moderately high. 



