22 BULLETIN 82, UNITED STATES NATIONAL, MUSEUM. 



to divide the space between these angles approximately into thirds. The muscular 

 fossfe are separated by a furrow, the diameter of which is about one-third the 

 diameter of the central canal. This furrow may carry a rounded carination in the 

 median line, on the highest part of which are a few spicules. The greatest (in- 

 terior) height of the muscular fossa? is somewhat less than the greatest dorsoventral 

 height of the interarticular ligament fossa\ The distal diameter of the muscular 

 fossae is not quite so great as the proximal diameter of the interarticular liga- 

 ment fossae. 



The ventral surface of the radial pentagon is covered by a spongy calcareous 

 mass, very slightly concave on its surface, which reaches nearly to the upper edges 

 of the muscular fossae. The central canal is rather small. 



Diameter of radial pentagon at base, 4.7 mm.; height of articular face (meas- 

 ured along the inclination). 1.9 mm.; width, at transverse ridge, 2.2 mm.; distance 

 from center of rosette to middle of dorsal outer edge of radial, 2.2 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. 



ETJDIOCRINUS ORNATUS. 

 Figs. 29, 30, p. 20. 



The dorsal ligament fossa is rather low. between three and four times as broad 

 as high. The proximal border is but slightly convex, at either end turning upward 

 in a moderately broad curve to the ends of the transverse ridge. The ligament pit 

 is rounded oval, about as large as the central canal. 



The ends of the transverse ridges of adjacent articular faces are entirely sep- 

 arated from each other, though the distance between them is small. The dorsal 

 ligament fossae are well separated : distal to the transverse ridge the articular faces 

 are separated by a narrow interradial groove which slowly increases in width 

 distally. 



The outer edges of the interarticular ligament fossae slope inward at an angle 

 of about 45 and continue this direction until they reach a length nearly or quite 

 equal to the distance from the central canal to the end of the transverse ridge. 

 They then turn inward, and this anterior or distal border takes a direction toward 

 the opposite side of the transverse ridge (on the other side of the central canal) 

 until about two-thirds of the distance to the perpendicular passing through the 

 nearer end of the central canal is accomplished, when it turns rather abruptly 

 downward, reaching a point just above the central canal, but at the side of the 

 median axis of the joint face. 



A narrow but rather deep intermuscular furrow reaches to the upper border of 

 the central canal. The sides of the interarticular ligament fossae which border this 

 furrow are somewhat thickened. 



The muscular fossae are much reduced and crescentic. The outer edge of the 

 interarticular ligament fossae is continued in the same direction as the outer edge 

 of the muscular fossae, but almost immediately begins to curve gradually inward, 

 the radius of the curve gradually shortening until it bends downward into the inner 



