MONOGRAPH OF THE EXISTING CRINOIDS. 



47 



nearly as far apart as the dorsoventral diameter of the central canal ; their proxi- 

 mal edges are delimited by the raised distal inner edges of the interarticular 

 ligament fossae, and make an angle of about 30° with the inner edges; the inner 

 edges are about one-third longer than the proximal edges: the distal edges, con- 

 necting the inner and the proximal edges, make a very full curve, in some cases 

 almost or quite a semicircle. The muscular fossae are inwardly separated by a 

 shallow furrow which runs up to the level of the distal angles of the interarticular 

 ligament fossae; beyond the end of this furrow the muscular fossae are separated 

 merely by a gap ; this furrow is outwardly bordered by the raised inner edges of 

 the muscular fossae, and along its center carries a median ridge of the same width 

 and height. 



There is no calcareous deposit on the ventral surface of the radials. 



Diameter of radial pentagon at base, 4.5 mm.; height of articular face (meas- 

 ured along the inclination), 2.4 mm.; width, at transverse ridge, 2.3 mm.; distance 

 from center of rosette to middle of dorsal outer edge of radial. 2 mm. ; diameter of 

 ventral interarticular space, 1.5 mm. 



PARAJIETRA ORION. 

 Figs. 74, 75, p. 43. 



The plane of the joint face elements distal to the transverse ridge at first 

 makes an angle of 45° with the dorsoventral axis, but the muscular fossae gradually 

 curve upward beyond the middle, becoming almost parallel witli the dorsoventral 

 axis, and turning outward rather abruptly at the tip : the dorsal ligament fossa 

 is not quite in the same plane as the other joint face elements, making with them 

 a very broadly obtuse angle. The rim about the central canal is high, prominent, 

 and rather broad. The radial faces are separated from each other in the inter- 

 radial angles by very narrow slits which extend downward almost to the trans- 

 verse ridges. ,- u i 



The dorsal ligament fossa? are low, about three times as broad as long, slightly 

 convex proximally, very broadly rounded at either end so as to appear more or 

 less semielliptical.' They are entirely separated from their neighbors, but the ends 

 of the transverse ridges of adjacent joint faces meet interradially. 



The interarticular ligament fossae are in the form of equilateral triangles, 

 with the interior angles broadly truncated by the rim about the central canal. 

 The outer and distal borders are rather prominently raised. 



The muscular fossa; are long and narrow, inwardly about four, outwardly 

 about three, times as long as broad. The inner .and outer edges are almost parallel, 

 the latter being only very slightly concave; the distal ends are well rounded. In- 

 wardly the muscular fossa; are separated by a narrow double ridge, which at first 

 is as high as the distal portion of the rim about the central canal but gradually 

 decrease! in height and soon becomes low, composed of the upturned and appressed 

 inner edges of the muscular fossa;. 



There is no calcareous deposit on the ventral surface of the radials. 



