MONOGRAPH OF THE EXISTING CKINOIDS. 65 



from center of rosette to middle of dorsal outer edge of radial. 1.3 mm. ; diameter 

 of ventral interarticular space, 0.2 mm. to 0.4 mm. 



The preceding description is based upon a comparative study of 10 specimens. 



In five larger specimens the narrow septum forming the distal border of the 

 interarticular ligament fossee, instead of being straight and making an angle of 

 about 40 with the transverse ridge as in those just described, makes a broad curve, 

 and in the outer portion becomes parallel to the transverse ridge. The outer border 

 of the muscular fossae also is more convex, and the intermuscular notch is less deep 

 and less variable in form. 



Height of articular face (measured along the inclination), 2 mm.; width, at 

 transverse ridge, 1.8 mm.; diameter of ventral interarticular space, 0.4 mm. 



TRICHOMETRA CUBENSIS. 

 Figs. 90, 100, p. 62. 



The radial articular faces of this species are essentially like those of Hathro- 

 metra tenella. 



The chief differences are that the outer edge of the interarticular ligament 

 fossae is nearly straight instead of strongly concave; the distal edge of the inter- 

 articular ligament fossse, which is straight, makes a somewhat less angle with the 

 transverse ridge ; and the muscular f OSSEB have both the proximal outer and distal 

 angles broadly and equally rounded, the outer border between them being slightly 

 concave; the intermuscular notch is only slightly indicated. 



Diameter of radial pentagon at base, 2 mm. ; height of articular face (meas- 

 ured along the inclination), 1.2 mm.; width, at transverse ridge, 1.1 mm.; diameter 

 of ventral interarticular space, 0.3 mm. 



NAXOMETRA BOWERSI. 

 Figs. 106, 107, p. 67. 



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

 proximal border rather strongly flattened. The ligament pit is only faintly 

 indicated. 



The articular faces are separated inter-radially by a narrow shallow groove of 

 uniform width, which is about half as broad as the central canal. The transverse 

 ridges of adjoining joint faces are in contact with each other, but the interradial 

 groove is not bridged by the muscular fossse. 



The interarticular ligament fossse are approximately equilateral triangles, with 

 their inner angles broadly truncated. Their distal border is only faintly indicated 

 by a very narrow, almost obsolete, ridge. 



The intermuscular septum is rather broad, with parallel sides, and is never 

 much raised above the general level of the muscular fossae. 



The muscular fossse are slightly less in height than the distance from the distal 

 angle of the interarticular ligament fossee to the proximal border of the dorsal 



