II I i.i |\ B2, l M I Kl) STATES NATIONAL MUSEUM 



tion of young comatulids, though in mosl fully grown individuals it is filled in by the 

 Bubsequeni development of the proximal pinnules. 



MUSCULAR ARTICULATIONS 



Gislen studied in greal detail the brachial articulations of the crinoids and their 

 significance, his conclusions differing somewhat from mine. He pointed out that 

 when examining the obliqueness of an articulation two different kinds of obliquity 

 must be distinguished. If an arm be viewed from the dorsal side it is noticed at 

 once that the lines that mark the articulations do not run at right angles to the longi- 

 tudinal axis of the arm, but cross the arm more or less obliquely. This Gislen called 

 exterior obliqueness. On the articular faces of the brachials the dorsoventral crest 

 and the transverse (fulcral) ridge do not usually meet at a right angle, with the 

 result that the muscles and interartieular ligaments of the two sides are not of the 

 same si/e. This he called interior obliqueness. 



raighl muscular articulation is characterized by two points of contact at the 

 same distance from the mediodorsal line; an oblique muscular articulation has a 

 distinct dorsolateral point of contact, and a less distinct ventrolateral one. This 

 difference is obvious only in those types in which the course of the articular lines 

 across the dorsal surface of the arm is fairly oblique; in those comatulids in which the 

 articular lines run nearly at right angles to the longitudinal axis of the arm it is in- 

 distinct, or not visible at all. As this feature stands in a certain relation to the 



rior obliqueness of the brachials, Gislfin believed that there would be a certain 

 amount of interest in ascertaining the degree of obliqueness in the course of the 

 articular lines across the dorsal side of the arms in the comatulids. 



I a parvula, arms 45 mm. long: (15) 1 17 brachials 1.1 mm. broad in each 



III mm. in the proximal part of the arm, and (12) 15 brachials 0.6 mm. broad in the 

 distal; relation of longer side of the brachials to width 1:1 to 3:2 angle of the distal 

 articulations with the longitudinal axis of the arm 66-72°. 



( •; peregrina mflgnifica, arms 160 mm. long: (9) 12 brachials 2.5 mm. 



■! in each lit mm. in the proximal part of the arm, and (12) 16 brachials 1.2 mm. 

 broad in the distal; relation of Longer side of the brachials to width 1:2 to 2:3; angle 

 of the distal articulations with the longitudinal axis of the arm 69-77°. 



Cmnntula Solaris, arms 100-f-mm. long: (9) 10 brachials 3.5 mm. broad in each 

 10 mm. in the proximal part of the arm, and (13) 15 brachials 2.0 mm. broad in the 



'; relation of longer side of the brachials to width 1:2; angle of the distal artic- 

 ulations with the longitudinal axis of the arm 72-76°. 



Coii.atuhi ptrtinata, arms 70 mm. long: Relation of longer side of the brachials 

 to width 2:3; angle of the distal articulations with the longitudinal axis of the arm 

 -,: 79°. 



' Waster sentosa, arms so mm. long: (11) 11 brachials 2.4 mm. broad in each 

 10 mm. in the proximal part of the arm, and (13) 15 brachials 1.7 mm. broad in the 

 distal: relation of longer side of the brachials to width 1:2; angle of the distal articu- 

 lations with the longitudinal axis of the arm S0-S9°. 



i antkeria delicatq grandis, arms 105 mm. long: (7) 8 brachials 3.0 mm, 



d in each to mm. in the proximal part of the arm, and (11) 14 brachials 1.3 mm. 



1 The flciir<-' In parentheses show the number nf jefrments when the syrycftil pairs art> counted as units. 



