A MONOGRAPH OF THE EXISTING CRINOIDS . 65 



The 10 arms are 65 mm. long. ~P t is the longest pinnule, and is stiffened. P 2 is 

 similar, but slightly shorter. P 3 is similar, but is slightly shorter than P 2 . The ends 

 of the segments of these proximal pinnules tend to be slightly prominent. 



The general appearance of the animal is strikingly like that of Tropiometra 

 carinata. 



Prof. F. Jeffrey Bell described Antedon bidens from Torres Straits as follows: 



Centrodorsal prominent: about 20 cirri, with about 20 joints, a number of which have two 

 minute processes on their dorsal side; the penultimate spine is small; none of the joints are distinctly 

 longer than broad, but a number of them have a shallow lateral excavation along their distal edge. 



First radials just visible; second very wide, in contact; third almost triangular, not quite twice 

 as long as the second, and forming a convex protuberance with it. Ten arms. First brachials in 

 contact, a little wider on their outer than their inner side, as are also the second brachials, which 

 form with the first a convex protuberance; the third brachials, which are syzygies, have a sharp distal 

 edge, as have the succeeding joints; these soon become wedge-shaped, and form a strong overlap 

 on either side alternately; after some time this diminishes, and the more terminal joints of the arm 

 form rather bead-like swellings on either side. 



Syzygies 3, 9, 14; 4-6 joints between the succeeding syzygies. 



The first pinnule is very stiff and long, with the most proximal joint the longest; it is placed on 

 the second brachial, has some 12 joints, of which the more basal are much longer than broad, and 

 which are also stouter than those on the sixth brachial, which, again, are a little stouter than those on 

 the fourth. The pinnules then gradually diminish in size, and then again increase further out. 



The arms are stiff, and somewhat compressed from side to side; they are about 45 mm. long; 

 diameter of disk 5 millim., of centrodorsal 3.3; length of cirri about 8 millim. 



The original colour was probably purple. 



Torres Straits. 



I examined Bell's specimens of Antedon bidens at the British Museum in 1910. 

 They represent the same species as the types of Lamarck's Comatula adeonae. In the 

 best specimen obtained by the Alert the cirri are about XX, 21. The bidentate 

 appearance is caused by the moving back of the transverse ridge so far that it is near 

 the proximal ends of the segments, while the distal dorsal edge of the segments has 

 become prominent, so that there are in effect two transverse ridges, appearing as two 

 small spines in lateral view. 



PI is the longest pinnule, and is considerably stiffened. P 2 is similar, but slightly 

 shorter. P 3 is similar, but slightly shorter than P 2 . The distal ends of the segments 

 of these lower pinnules tend to become slightly prominent. 



This specimen is similar to that from Alert station 87 described above. 



Prof. Ludwig Doderlein recorded and gave notes on several specimens from 

 Thursday Island : 



He said that the dorsal pole of the centrodorsal is tuberculated 



The cirri are about XX, 20-22, up to 12 mm. long. The proximal segments are 

 cylindrical, and the distal are strongly compressed. The five basal segments are 

 somewhat broader than long, and the remainder are as long as broad. From about 

 the fourth onward each segment bears dorsally a transverse furrow that extends 

 somewhat on to the sides. As a result of this furrow each segment when seen from 

 the side appears to possess two dorsal tubercles or points, which are very characteristic 

 of this species. The opposing spine is weak. The terminal claw is moderately 

 strongly curved. 



The radials are just visible. The IBr, are very broad, and arc in lateral contact. 



