14 BULLETIN 82, UNITE!) STATES NATIONAL, MUSEUM. 



straight or slightly convex; the inner distal corners are well rounded; the inner 

 sides are parallel and are separated by a rather broad, shallow, intermuscular 

 furrow, somewhat wider than the transverse (greater) diameter of the central 

 canal. 



The muscular fossa? are narrow, about as broad as the dorsoventral diameter 

 of the central canal, or slightly broader, with their distal edges parallel to the 

 distal edges of the interarticular ligament fossa?: their inner edges are well 

 rounded and project somewhat farther into the intermuscular furrow than the 

 inner angles of the interarticular ligament fossse; the outer distal angles are more 

 sharply rounded and project beyond the corresponding angles of the interarticular 

 ligament fossa?. 



The central portion of the ventral surface of the radial pentagon is occupied 

 by a very coarse calcareous reticulation the meshes of which are somewhat more 

 dense than is usually the case. 



Diameter of radial pentagon at base, 3 mm.; height or articular face, 1.4 

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

 angle. 1.3 mm. 



COMACT1NIA F.CHINOPTERA. 



riss. in. 20. 2?,, 24, p. 15. 



The dorsal ligament fossa is about three times as broad as high, with the 

 proximal border broadly and evenly curved; the ligament pit is oval, consider- 

 ably larger than the central canal. 



The transverse ridges of adjacent articular faces are in contact laterally; 

 the lateral ends of the adjacent dorsal ligament fossa? are also in apposition. The 

 interarticular ligament fossa? are separated in the interradial angles by a narrow 

 groove, which is continued outward between the muscular fossa?. 



The interarticular ligament fossa? are about one-third broader than high, 

 approximately oblong, with the inner distal angle rounded, sometimes broadly so. 

 The distal margin may be more or less convex, and the outer margin retreats 

 somewhat basally from the ends of the transverse ridge. The inner edges are 

 parallel and straight, about as far apart as the transverse (greater) diameter 

 of the oval central canal. 



The muscular fossae, which are comparatively large, are nearly as hich as 

 the interarticular ligament fossse. Their distal border is broadly convex ; their 

 inner borders straight and parallel, not much more than half as far apart as 

 those of the interarticular ligament fossae. Their outer border makes an angle 

 of nearly 30 with that of the outer edge of the interarticular licament fossae. 

 The chord of the distal convexity of the muscular fossas may be horizontal, or 

 inclined slightly inward. 



The ventral surface of the radial pentagon is entirely covered with a rather 

 coarse and loose calcareous deposit through which there is no special central canal. 



