MONOGRAPH OF THE EXISTING CKINOIDS. 21 



The muscular fossae are separated by a shallow groove about as wide as their 

 inner downward extensions. This groove may be more or less carinate at the 

 bottom. The inner edge of the muscular fossae is about as long as the distal, 

 and is perpendicular to it. Both are about as long as the distance between the 

 inner distal angles of the interarticular ligament fossae and the transverse ridge. 

 The muscular fossae in shape resemble a boomerang, or broad gamma, the hori- 

 zontal limb being somewhat thicker than the vertical. 



The space between the radials ventrally is filled with an open calcareous 

 filling the surface of which is plane and on the same level with the distal edges 

 of the muscular fossa. It is covered with small papilla?. The central canal is 

 moderately small, as in C atoptometra hartlaubi. 



Diameter of radial pentagon at base, 4 mm.; height of articular face (meas- 

 ured along the inclination), 1.7 mm.; width, at transverse ridge, 2.1 mm.; distance 

 from center of rosette to middle of dorsal outer edge of radial, 1.9 mm.; dis- 

 tance from center of ventral face of radial pentagon to middle of outer ventral 

 face of radial, 1 mm.; to apex of interradial angle, 1.3 mm. 



CATOPTOMETRA HARTLAUBI. 

 Figs. 32, 33, p. 20. 



The dorsal ligament fossa is narrow, about four times as broad as long. 

 The proximal edge is comparatively slightly convex, and the lateral angles are 

 truncated, so that lateral edges are formed which are about half as long as the 

 median diameter of the dorsal ligament fossa, or slightly longer. 



The interarticular ligament fossae are about as high as broad, the height 

 being about equal to that of the dorsal ligament fossa. The lateral edges 

 retreat sharply from the transverse ridge, taking the same general direction 

 as the lateral edges of the dorsal ligament fossa, and, like them, being more 

 or less concave, rather more prominently so than they. The inner angle is 

 broadly truncated by the rim about the somewhat large central canal. The inner 

 edges run outward and upward at an angle of about 45 to a point slightly be- 

 yond the middle of the horizontal portion of the distal edge, then curves and 

 runs almost or quite parallel to the transverse ridge to the outer edge. The 

 distal inner corners of the interarticular ligament fossae are separated by the 

 distance equal to the horizontal diameter of the central canal. 



The muscular fossae may be described as forming roughly a right-angled tri- 

 angle, the distal edge forming the base, with the hypothenuse concave (being formed 

 by the distal edge of the interarticular ligament fossae) , the angles broadly rounded, 

 and the base somewhat convex. The greatest (innermost) height is about one- 

 third less than the greatest horizontal diameter. The distal edges are slightly 

 convex or almost straight, running in a general horizontal direction, outwardly 

 curving downward to the distal outer corner of the interarticular ligament fossae, 

 inwardly, with a similar or somewhat broader curve, running into the parallel inner 

 edges which reach the raised rim about the central canal between, and slightly 

 above, the inner distal angles of the interarticular ligament fossae, in such a way as 



