MONOGRAPH OF THE EXISTING CRIKOIDS. 39 



higher exteriorly and lower interiorly. The inner portion of the radial pentagon 

 has but little secondary calcareous deposit, and there is none on the ventral surface 

 of the rosette. The interior of the radial pentagon is well rounded and is scored 

 with shallow narrow meandering grooves. 



Diameter of radial pentagon at base, 10.6 mm.; height of articular face 

 (measured along the inclination), 3.7 mm.; width, at transverse ridge, 5.5 mm.; 

 distance from center of rosette to middle of dorsal outer edge of radial, 5 mm. : dis- 

 tance from center of ventral face of radial jDentagon to middle of ventral edge of 

 radial, 1.9 mm. ; to apex of interradial angle, 2.8 mm. 



TROPIOMETRA ENCRINUS. 

 Figs. 60, 61, p. 33. 



The dorsal ligament fossa is very narrow, about four times as broad as high, 

 regularly elliptical. The ligament pit is considerably broader than the central 

 canal, transversely elongate, but only slightly marked. 



From either end the transverse ridge gradually thickens so that it increases 

 in breadth to the middle, where it encompasses the central canal; this increase in 

 diameter is very even, so that only a very slight broad concavity of the anterior 

 borders on either side of the central canal is discernible. 



A narrow and shallow intermuscular furrow i-uns outward from the distal 

 portion of the rim about the central canal, which is usually not quite so broad as 

 half the width of the canal ; its sides are parallel, or very slightly divergent. 



The distal border of the interarticular fossae is parallel to the transverse ridge, 

 and shows a slight convexity near the intermuscular furrow. The proximal part 

 of the low septum forming the distal border begins to curve gradually downward 

 at about half the distance from the outer border to the intermuscular furrow, join- 

 ing the distal border of the transverse ridge to one side of the perpendicular pass- 

 ing through the lateral border of the central canal, usually about as far distant as 

 the dorsoventral (lesser) diameter of the central canal. The height of the inter- 

 articular ligament fossse is a little less than that of the dorsal ligament fossa. 



The muscular fossae are large and well rounded; they are about twice the 

 height of the interarticular ligament fossae. The distal margin may be a broadly 

 rounded triangle with the apex near the outer side, or it may be nearh' trapezoidal 

 with the inner distal angle more rounded than the outer. The lower inner corners 

 of the muscular fossae are occupied by a supplementary muscle plate which rises 

 rather suddenly to about half the height of the interarticular ligament fossEe, makes 

 a broad curve and extends outward and downward nearly in a straight line to the 

 distal outer angle of the interarticular ligament fossaa. The inner portion of the 

 distal border of the interarticular ligament fossae is frequently depressed almost 

 to the proximal edge of this distal border, and this sunken area is somewhat raised 

 in the center and convex on the outer edge, so that it becomes a second supple- 

 mentary muscle plate resembling that seen in Perometrn diomedea'. 



There is no calcareous deposit on the inner surface of the radial pentagon or 

 upon the ventral surface of the rosette. 

 142140— 21— Bull. 82 5 



