MONOGRAPH OF THE EXISTING CRINOIDS. li 



so that, viewed interraclially, they are seen to be separated by a narrow U reaching 

 downward nearly to the transverse ridge. Their distal edges, which are straight 

 or very slightly convex and parallel to the transverse ridge, run inward for a dis- 

 tance equal to between one-half and three-quarters of the height of the interarticular 

 ligament fossae, then sweep downward in the form of a concave margin to the 

 upper part of the central canal ; this margin is usually more or less irregular. The 

 space between the interarticular ligament fossae is very broadly U-shaped to semi- 

 circular, and is somewhat larger than the adjacent part of the interarticular liga- 

 ment fossae. It is only slightly depressed below the general surface, and is marked 

 with more or less irregular strong longitudinal (dorso ventral) striations, which are 

 continuations of the radiating striations on the ventral surface of the radial 

 pentagon. 



The muscular fossae are linear and narrow, lying along the distal edge of the 

 interarticular ligament fossae and just rounding their inner distal angles. 



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

 mass marked ventrally with more or less regular fine radial striations which reach 

 to the height of the distal border of the muscular fossae. The central canal is 

 moderately large. 



Diameter of radial pentagon at base, 6.1 mm. ; height of articular face, 2.5 mm. ; 

 width, at transverse ridge, 4 mm.; distance from center of rosette to middle of 

 dorsal outer edge of radial, 2.8 mm.; distance from center of ventral surface of 

 radial pentagon to middle of ventral outer edge of radial, 2.3 mm. ; to apex of 

 interradial angle, 3 mm. 



COMASTER PAI5VUS. 

 Figs. 25, 26, p. 20. 



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

 proximal border regularly elliptical. The ligament pit is transversely oval, and 

 about as large as the central canal. 



The ends of the transverse ridges of adjacent joint faces are joined, but the 

 dorsal ligament fossae are widely free ; the joint face elements distal to the trans- 

 verse ridge are separated by a broad shallow V-shaped gap. 



The outer borders of the interarticular ligament and muscular fossae make an 

 angle of about 60 with the transverse ridge. The edges of the interarticular 

 ligament fossa? are more or less concave. The maximum (outer) height of the 

 interarticular ligament fossae is about equal to that of the dorsal ligament fossa. 

 From the outer distal angles the distal edges of the interarticular ligament fossae 

 run inward and slightly downward to the intermuscular furrow, which they join 

 at a point about as high above the distal border of the central canal as the hori- 

 zontal (greater) diameter of the canal. They may be nearly straight, evenly 

 convex, or nearly straight outwardly and becoming more convex inwardly. If the 

 convexity is strong they may join the intermuscular furrow at a point above the 

 distal border of the central canal about as far distant as the median (shorter) 

 diameter of the canal. 



