MONOGRAPH OF THE EXISTING CRINOIDS. 35 



Diameter of radial pentagon at base, 3.8 mm.; height of articular face 

 (measured along the inclination), 1.5 mm.: width, at transverse ridge, 2 mm.; 

 distance from center of rosette to middle of dorsal outer edge of radial. 1.9 mm. ; 

 distance from center of ventral surface to middle of ventral outer edge of radial. 

 0.9 mm. ; to apex of interradial angle, 1.2 mm. 



COLOBOMETRIDJE. 



The articular faces of the radials lean inward so that the plane of the inter- 

 articular ligament fossae makes an angle of nearly or quite 60 with the dorsoventral 

 axis of the animal; the plane of the muscular fossae, however, is nearly or quite 

 parallel with the dorsoventral axis, and thus makes an angle of approximately 

 120 with the plane of the interarticular ligament fossae. 



In Cenometra, which in many ways approaches the genera of the Mariametridae, 

 the conditions found in the radial articular faces are not greatly different from 

 what is found in that family. 



The excavation of the various elements of the joint faces is. except in 

 Cenometra, deep, and the anterior border of the transverse ridge and the rim about 

 the central canal are high and well marked, though not particularly narrow. 



The elements on either side of the transverse ridge are in the same plane in 

 Cenometra, but in the other genera the dorsal ligament fossa makes a lesser angle 

 with the dorsoventral axis than the interarticular ligament fossae. 



The dorsal ligament fossa is large and deep, with the proximal border well 

 rounded. The ligament pit is strongly marked and more or less circular, its area 

 being usually approximately that of the central canal. 



The central canal is oval or nearly circular, moderate in size or rather large. 



The intermuscular furrow has parallel, slightly converging, or slightly diverg- 

 ing sides; it is never broader than the transverse diameter of the central canal. 

 In one genus it is replaced basally by a narrow intermuscular septum which at 

 first is high, but rapidly decreases in height distally, and in the outer part passes 

 over into a narrow intermuscular septum. 



In Cenometra the distal edge of the interarticular ligament fossae is slightly 

 convex, the chord of the convexity being slightly lower interiorly than exteriorly. 

 In the other genera it is straight and runs downward and inward, usually at an 

 angle of about 60 to the transverse ridge, to the distal portion of the rim about 

 the central canal. In Oligometra the angle between the transverse ridge and the 

 distal borders of the interarticular ligament fossae is only about 45, and the inner 

 distal angle of the interarticular ligament fossae is more or less indicated. 



The muscular fossae are very variable. In Cenometra. they are very narrow, 

 about as wide as the dorsoventral (shorter) diameter of the central canal, and 

 their distal borders are parallel to the distal borders of the interarticular ligament 

 fossae. The outer distal angles project beyond the outer distal angles of the inter- 

 articular ligament fossae, as in the Mariametridae, and the inner angles are inserted 

 just within the inner distal angles of the interarticular ligament fossse; they 



