14 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



tion of young comattdids, though in most fully grown individuals it is filled in by the 

 subsequent development of the proximal pinnules. 



MUSCULAR ARTICULATIONS 



Gislen studied in great 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 (fulcra!) ridge do not usually meet at a right angle, with the 

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

 same size. This he called interior obliqueness. 



A straight 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 aU. As this feature stands in a certain relation to the 

 exterior obliqueness of the brachials, Gisleu 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. 



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

 10 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. 



Comissia peregrina magnified, arms 160 mm. long: (9) 12 brachials 2.5 mm. 

 broad in each 10 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. 



Comatula Solaris, arms 100+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 

 distal; 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. 



Comatula pectinata, 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 

 67-79. 



Capillaster sentosa, arms 80 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 80-89. 



Comantheria delicata grandis, arms 105 mm. long: (7) 8 brachials 3.0 mm. 

 broad in each 10 mm. in the proximal part of the arm, and (11) 14 brachials 1.3 mm. 



1 The figures in parentheses show the number of segments when the syzygial pairs are counted as units. 



