76 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



articular ligament fossse does not reach tbe outer edge of the joint face; 

 the inner halves of the free borders of the muscular fossae slope inward 

 and downward at an angle of about 90° with each other, forming a broad 



right-angled notch Erythrometra ruber. 



f. The outer borders of the interarticular ligament and muscular fossa; form a 

 discontinuous line which is almost straight but slightly indented at the 

 junction of the fosssB; the ridge forming the distal border of the inter- 

 articular ligament fossse reaches the outer edge of the joint face; the 

 distal borders of the muscular fossic are nearly straight and parallel with 



the transverse ridge Compsometra lovdni. 



;»'. The muscular fossae are much larger than the interarticular ligament fossae. 



i\ The outer borders of the interarticular ligament and muscular fossae form 



continuous straight lines and are nearly parallel ; the distal borders of the 



muscular fosste are flattened and parallel to the transverse ridge; the 



intermuscular notch is small and shallow, well rounded proximally. 



Hypalometra defccta. 

 i'. The outer borders of the interarticular ligament and muscular fossie are 

 discontinuous, both being strongly convex, or those of the muscular fossa- 

 strongly convex and those of the interarticular ligament foss.'e straight; 

 the distal borders of the muscular fossae are strongly rounded; the inter- 

 muscular notch is deep and sharply pointed proximally. 

 p. The intermuscular septum is relatively broad and is expanded proxi- 

 mally just over the central canal; the outer borders of the interarticular 

 ligament fossae are straight; the muscular fossie are rounded triangular, 

 their outer borders being more or less flattened and converging to the 



well-rounded distal angles Thaumatometra tenuis. 



j'. The intermuscular septum is high and very narrow, and it is not expanded 

 basally; the outer borders of the interarticular ligament fossae are 

 strongly convex ; the muscular fossa; are much more broadly I'ounded, 



especially distally Pentametrocrinus. 



fc\ Tlie muscular fossae are very broad, the maximum width being more 

 than three quarters of the maximum (inner) height; the outer bor- 

 ders of the interarticular ligament fossae form a continuous curve 

 with the border of the dorsal ligament fossse. 



Pentametrocrinus japonicus. 

 k'. The muscular fossae are narrower, the maximum height being not much 

 more than twice the maximum width ; the maximum height of the 

 convexity of the lateral borders of the interarticular ligament fossae 

 extends to beyond the ends of the transverse ridge, which lie in a 

 rounded concavity between the borders of the interarticular and 



dorsal ligament fossae Pentametrocrinus semperi. 



g'. The height of the articular faces is much greater than the length of the trans- 

 verse ridge. 

 h'. The muscular fossae are high and narrow, more than twice as long interiorly 

 as their maximum width, 

 i'. The plane of the muscul.Tr fossae is almost parallel to the dorsoventral axis 

 of the animal, while tlie plane of the interarticular ligament fossae makes 

 a considerable angle with it, the latter therefore leaning inward at a 

 greater angle than the former; the outer distal angle of the interarticular 

 ligament fossae reaches a height equal to about one-third of the distance 

 from the inner proximal to the inner distal angles of the muscular foss.i' : 

 the centrodorsal is long, columnar, with the cirrus sockets in 5 pairs of 

 regular columns which are separated by high ridges. 



Zenometra columnaris. 



