MONOGRAPH OF THE EXISTING CRINOIDS. 63 



In the interradial angles the articular faces are separated, proximal to the 

 lower fourth of the mascular fossae, by a triangular space, slightly excavated, the 

 sides of which make with each other an angle of about 30, the apex lying at the 

 distal end of the proximal fourth of the muscular fossae. The sides are straight 

 and regularly divergent as far as the transverse ridge; they then very gradually 

 begin to turn, passing over into the curved proximal borders of the dorsal liga- 

 ment fossae. 



The interarticular ligament fossae are small, and scarcely equal in height the 

 dorsal ligament fossa; the outer half of their distal border is nearly or quite 

 parallel to the transverse ridge; the inner half curves gradually downward, so 

 that it joins the rim about the central canal at an angle of about 45. 



The intermuscular septum is low and comparatively broad, extending distally 

 to the intermuscular notch. At first it decreases in height rapidly, then more 

 gradually. 



The maximum height of the muscular fossae is equal to that of the dorsal liga- 

 ment and the interarticular ligament fossae combined. They are separated in- 

 teriorly by a broad and deep intermuscular notch, rounded proximally, which 

 extends downward for two-fifths, or even one-half, of the distance from the outer 

 border to the distal rim about the central canal. They are very broadly rounded. 



The joint face elements on either side of the dorsoventral plane distal to the 

 transverse ridge make with each other a much broader angle than usual, the angle 

 approximating 120, so that the excavation of the reentrant angles of the ventral 

 star of the radial pentagon is comparatively slight. The outer three-fourths of the 

 muscular fossae lie in a plane parallel to the dorsoventral axis of the animal. 



There is no deposition of calcareous matter on the inner sides of the radials. 



Diameter of radial pentagon at base, 4.3 mm. ; height of articular face (meas- 

 ured along the inclination), 2.5 mm.; width, at transverse ridge, 2 mm.; diameter 

 of ventral interarticular space, 2 mm. 



BATHYMETRINJE. 



HATHROMETRA PROLIXA. 

 Fig. 101, p. 62. 



The dorsal ligament fossa is more flattened proximally than in H. tenella. 



The interarticular ligament fossse are only partially separated from the mus- 

 cular fossae distally. The septum is of the same character as that in H. tenella, 

 but it rapidly decreases in height and terminates halfway between the rim about 

 the central canal and the outer edge of the joint face. The outer edge of the area 

 occupied by the interarticular ligament, instead of being strongly concave as in 

 H. tenella, is convex. 



The muscular fossae are longer and narrower than in H. tenella, being one- 

 third longer than the distance from the inferior border of the dorsal ligament fossa 

 to the distal border of the interarticular ligament fossae. The outer edge of the 

 muscular fossae is slightly concave, or nearly straight. 



