76 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



articular ligament fossa? does not reach the outer edge of the joint face; 

 the inner halves of the free borders of the muscular fossa? slope inward 

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



right-angled notch ErytJiromrtra ruber. 



f. The outer borders of the iuterarticular ligament and muscular fossa? form a 

 discontinuous line which is almost straight but slightly indented at the 

 junction of the fossa?; the ridge forming the distal border of the inter- 

 articular ligament fossa? reaches the outer edge of the joint face; the 

 distal borders of the muscular fossa? are nearly straight and parallel with 



the transverse ridge Gompnoinetru lop&ni. 



h*. The muscular fossa? are much larger than the iuterarticular ligament fossa?. 



P. The outer borders of the interarticular ligament and muscular fossa? form 



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



muscular fossa? are flattened and parallel to the transverse ridge; the 



intermuscnlar notch is small and shallow, well rounded proximally. 



ffypalometra defecta. 



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

 discontinuous, both being strongly convex, or those of the muscular foss;v 

 strongly convex and those of the interarticular ligament fossie straight; 

 the distal borders of the muscular fossa? are strongly rounded; the inter- 

 muscular notch is deep and sharply pointed proximally. 

 ;'. The Intermuscular septum is relatively broad and is expanded proxi- 

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

 ligament fossa? are straight; the muscular fossa? are rounded triangular, 

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



well-rounded distal angles Thaumatometra tennis. 



f. The intermnscular 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 fossse are much more broadly rounded, 



especially distally Pentametrocrinus. 



A-. 1 . The muscular fossse are very broad, the maximum width being more 

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

 ders of the interarticular ligament fossa? form a continuous curve 

 with the border of the dorsal ligament fossse. 



Pcntnmetroci'inus japon /CMS. 



k'. The muscular fossa? 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 fossse 

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

 rounded concavity between the borders of the interarticular and 



dorsal ligament fossa? Pentametrocrinus scmperi. 



g 1 . The height of the articular faces is much greater than the length of the trans- 

 verse ridge. 

 ft 1 . The muscular fossse are high and narrow, more than twice as long interiorly 



as their maximum width. 



i 1 . The plane of the muscular fosste is almost parallel to the dorsoventral axis 

 of the animal, while the plane of the interarticular ligament fossa? makes 

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

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

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

 from the inner proximal to the inner distal angles of the muscular fossa- : 

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

 regular columns which are separated by high ridges. 



Zenometra cnlumnaris. 



