MONOGRAPH OF THE EXISTING CKINOIDS. 



73 



c*. The muscular fossa? are at least as large as, and usually much larger than, the inter- 

 articular ligament fosses. 

 d 1 . The total height of the articular fossae is much less than the length of the transverse 



ridge. 



c- 1 . The distal borders of the iuterarticnlar ligament fossa; run in a broad curve from 

 the distal border of the central canal outward and upward to the distal outer 

 angles of the joint face; as the distal border of the joint face is only slightly con- 

 cave the muscular fossa 1 are highest interiorly and taper to a point resting on the 

 outer distal angles of the interarticular ligament fossae. 



ComatiJia iridoiiietriformis. 

 e?. At least the distal half of the outer borders of the joint face is formed by the edges 



of the muscular fossa 1 . 



f. The distal borders of the interarticular ligament fossae are more or less decurved 

 in their outer halves or two-thirds, so that the muscular fossse are higher out- 

 wardly than inwardly; there are no supplementary muscle plates or bosses in 

 the inner proximal angles of the muscular fossse. 



1 . The muscular fossa? are about twice as large as the interarticular ligament 

 fossie: the distal borders of the interarticular ligament fossa? are very 

 strongly convex; the proximal halves of the muscular fossa? are separated 

 interiorly by the distal portion of a broad elevated triangular structure of 

 which the strongly convex base reaches nearly to the central canal, and the 



distal halves by a narrow space with parallel sides Thi/sanometra tencUoides. 



g*. The muscular fossa; are about the same size as the interarticular ligament 

 fossa?; the distal borders of the interarticular ligament fossa} are only slightly 

 convex : the joint face elements are separated in the median line by a promi- 

 rnent furrow which is more or less constricted between the muscular fossa?. 



Leptoncmastcr venustun. 



f. The distal borders of the interarticular ligament fossae are straight and are usually 



directed more or less upward and outward so that the interarticular ligament 



fossa? are triangular and the inner proximal angle of the muscular fossa? is 



nearer the transverse ridge than the outer; a prominent supplementary muscle 



plate or rounded boss occupies the inner proximal angle of the muscular fossa 3 . 



(f. The distal borders of the muscular fossae are flattened and nearly parallel to 



the transverse ridge, or convex with the chord of the convexity parallel to the 



transverse ridge; a broadly rounded outer distal angle is always evident; the 



centrodorsal is well rounded in lateral view Antedon. 



/i 1 . The sides of the intermuscular furrow are parallel, or diverge slightly dis- 



tally. 

 t'. The outer distal angles of the muscular fossa? are very broadly rounded. 



Antedon pctasux. 

 f. The outer distal angles of the muscular fossa? are less broadly rounded. 



Antedon biftdu. 



ft*. The sides of the intermuscular furrow converge distally. 

 t 1 . Distal border of muscular fossa? strongly convex ; distal border of inter 

 articular ligament fosso? nearly parallel to the transverse ridge. 



Ante-don adriatica. 



f. Distal border of muscular fossa? flattened; distal border of interarticular 

 ligament fossa? running upward and outward, making a considerable angle 



with the transverse ridge Antedon mediterranea. 



g 1 . The distal borders of the muscular fossae are very broadly rounded without any 

 indication of a distal outer angle, or slope downward and inward to the end of 

 the intermuscular furrow ; the centrodorsal is a short cylinder Tropiometra. 



