MONOGRAPH OF THE EXISTING CKINOIDS. 13 



length. The distal edges are gently concave, the chord of the arc formed rising 

 slightly inwardly: at the inner corners the distal edges curve downward into the 

 inner edges: these inner edges from the distal to the proximal part of the inter- 

 articular ligament fossa; diverge slighth% proximately curving around and meet- 

 ing just above the central canal, over which the proximal end of the intermus- 

 cular furrow is somewhat convex, following the outline of the canal. The broad 

 shallow furrow separating the interarticular ligament fosste at the distal border 

 of the latter is about half as wide as they are at that point, or even slightly 

 wider. It increases slightly in width proximally; its center may be more or less 

 elevated. 



The muscular fossae are very narrow, with parallel sides and rounded ends. 

 Their width is about equal to the transverse (greater) diameter of the central 

 canal: their distal edges follow the curve of the distal border of the interarticular 

 ligament fossil : their rounded outer angle extends somewhat beyond the distal 

 outer angle of the interarticular ligament fossse; their inner termination extends 

 slightly beyond the inner distal angle of the interarticular ligament fossae so 

 that the intermuscular furrow is constricted at this point; their inner boundary 

 joins the rounded inner angle of the interarticular ligament fossae at about the 

 center of its curve. 



The ventral surface of the radial pentagon is covered with a moderately 

 dense calcareous deposit which shows faint radial striations. The central canal 

 is rather small. 



In the specimen at hand the general coloration is yellow brown, the transverse 

 ridges and the rays of the basal star being violet in conspicuous contrast. 



Diameter of radial pentagon at base, 4.6 mm.; height of articular face, 2 

 mm. ; width, at transverse ridge, 3 mm. ; distance from center of rosette to middle 

 of dorsal outer edge of radial, 2 mm.; distance from center of ventral face of 

 radial pentagon to middle of ventral outer edge of radial, 1.8 mm.; to angle 

 between radials, 2.5 mm. 



COMATtJLA MICRASTER. 



Figs. 15, 16, p. 15. 



The dorsal ligament fo.ssa is about two and one-half times as broad as high, 

 only slightly convex proximally, curved upward with moderate abruptness at 

 either end. The ligament pit is transversely oval, considerably larger than the 

 central canal. 



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

 ligament fossae are entirely separated. The elements distal to the transverse 

 ridge are separated in the interradial angles by a shallow furrow about as broad 

 as the shorter (vertical) diameter of the central canal. 



The interarticular ligament fossae are slightly higher than wide, approximately 

 oblong. The outer edges retreat rather rapidly for a short distance from the 

 ends of the transverse ridge, then becoming parallel to the dorsoventral axis, or 

 leaning slightly outward in the distal portion. The distal border is practically 



