A MONOGRAPH OF THE EXISTING CRINOIDS 657 



Syzygies between brachials 3 + 4, 11 + 12, 19 + 20; in variety 1, 3 arms. 



Syzygies between brachials 3 + 4, 11 + 12, 21 + 22; in variety 2, 2 arms. 



Syzygies between brachials 3 + 4, 12 + 13, 16+17; in the typical series, 3 arms. 



Syzygies between brachials 3 + 4, 12+13, 17 + 18; in the typical series, 33 arms; 

 in variety 1, 4 arms; in variety 2, 1 arm. 



Syzygies between brachials 3 + 4, 12+ 13, 18+19; in the typical series, 3 arms. 



Syzygies between brachials 3 + 4, 13 + 14, 16+17; in the typical series, 1 arm. 



Syzygies between brachials 3 + 4, 13+ 14, 18+19; in the typical series, 30 arms; 

 in variety 1, 1 arm; in variety 2, 1 arm. 



Syzygies between brachials 3 + 4, 13 + 14, 20 + 21; in the typical series, 1 arm. 



Syzygies between brachials 3 + 4, 14+ 15, 18+19; in the typical series, 1 arm. 



Syzygies between brachials 3 + 4, 15+ 16, 20 + 21 ; in the typical scries, 1 arm; in 

 variety 1, 1 arm. 



Carpenter pointed out that the normal position of the second syzygy is between 

 brachials 11 + 12, and that in those cases in which it does not occupy this position it is 

 much oftener between brachials 12 + 13 or 13+14 than between brachials 9+10 or 

 10+11; that is to say, that variation, when it occurs, is in the direction of increase 

 rather than of decrease in the length of the first intersyzygial interval. 



The number of muscular articulations in the first intersyzygial interval in 

 typical specimens and in varieties 1 and 2 is given for 222 arms by Carpenter, as 

 follows: 1 (once); 2 (twice); 3 (once); 5 (4 times); 6 (13 times); 7 (120 times); 8 (44 

 times); 9 (34 times); 10 (once); 11 (twice). 



The number of muscular articulations in the second intersyzygial interval in the 

 type series and in varieties 1 and 2 is given by Carpenter as follows: 1 (once); 2 (3 

 times); 3 (10 times); 4 (192 times); 5 (8 times); 6 (4 times) 7 (3 times); 9 (once). 



Carpenter wrote that after the sixteenth brachial the intersyzygial interval is 

 usually 4 muscular articulations. It is, however, very unusual to find an arm in which 

 this interval is constant throughout its whole length and does not vary to a greater or 

 lesser extent. In only 7 arms out of the total number which he examined did he find 

 this to be the case, together with normal first and second intersyzygial intervals, 

 although 23 other arms were regular from the second syzygj' onward. These 30 arms 

 were distributed among 5 of the 8 specimens in the type series, while in none of the 

 other 3 was the intersyzygial interval constant throughout the length of any of the 

 arms. 



The same was the case with the varietal specimens. In the typical form there is a 

 tendency to a decrease rather than to an increase in the length of the interval, which 

 is more often 3 muscular articulations than 5, while in varieties 1 and 2 the tendency 

 of the variation is to increase the length of the interval, 5 muscular articulations 

 occurring much more commonly than 3. 



Carpenter remarked that these conclusions are all based upon an examination of 

 single specimens, which may in some instances be very misleading. 



Carpenter said that Pj and the pinnules on the division series are very long and 

 slender, those on the division series being the longest, and are composed of 30-40 

 segments. The number of teeth in the comb varies from 10-12 on Pd to 6-8 on a 

 brachial pinnule. In cases where Pi is the lowest pinnule it is much longer than 

 usual, and more of its terminal segments bear teeth. 



