1 Q 



MONOGRAPH OF THE EXISTING CRINOIDS. ^^ 



inner halves are nearly parallel with the median axis of the joint face, and 

 their outer approximately at right angles to it. The vertical and horizontal 

 portions are united in a broad curve, in which the muscular fossa> attain their 

 maximum width. . . , 



The ventral face of the radial pentagon is pentagonal or decagonal in out- 

 line. The radial portions are not incised. 



The central plug mav cover only the inner ends of the radials, or it may 

 cover their entire inner surface and rise to the level of the distal edge of the 

 muscular fossae; it is coarser in structure in the center than toward the pe"phery, 

 but there is no free central canal. The radial canals, when not obscured by the 

 deposition of calcareous matter, are very broad. 



ZTGOMETRA COMATA. 



Figs. 27, 28, p. 20. 



The dorsal ligament fossa is between two and one-half and three tmies as 

 broad as the median length, evenly convex proximally, but at the corners bend- 

 ing upward rather more strongly so as to join the ends of the transverse ridge 

 approximately at a right angle. . 



The ends of the transverse ridges of adjacent joint faces are ]ust m apposition, 

 but the dorsal ligament fossa, are entirely closed and do not communicate laterally 



with each other. . j ^ „ „„fK„,. 



The outer edges of the interarticular ligament fossa- run inward at a rathei 

 small angle with the dorsoventral axis of the animal. They are usually more 

 or less concave, this concavity being most marked proximally and dying away 

 distally Just beyond the somewhat large transversely oval central canal is a 

 horizontal slightly .raised ridge about one-fourth or one-third again as broad as 

 the diameter of the central canal which marks the proximal border of the mus- 

 cular fossae. From the ends of this rim the inner edges of the interarticular liga- 

 nent fossa, run perpendicularly (parallel with each other) upward to a point 

 about as far from the ridge as that is from the nearest part of the dorsal hga- 

 ment fossa, then turn outward somewhat abruptly and run to the outer edge at 

 TsUght a^gle to the horizontal. The greatest (exterior) heigh of the inter^ 

 artT ular lijment fossa, is about equal to the greatest (proximal) width, which 

 itself is about equal to the maximum height of the dorsal ligament fossa. The 

 portions of the interarticular ligament fossa, beyond the centra canal are sepa- 

 rated by a rectangular gap equal in breadth to the diameter of the interarticular 

 li-rament fossa, at this point, and not quite twice as broad as long. 



Tlie distal ed-es of the muscular foss.c form a straidit line with each othei. 

 The outer corners%re curved downward to the outer distal angles of the inter- 

 ar cuTr ligament fossa,; the inner distal angles are rounded off. the inner edges 

 ben. paraUel and running to the ridge mentioned above as just beyond the 

 central canal. The inner edges of the muscular fossa, reach this ridge in such 

 a way as to divide the space between the interarticular ligament foss^ into thirds. 



