538 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



Pi 8 mm. long, moderately stout basally, but tapering rapidly in 

 the proximal half and becoming very slender and thread-like distally, 

 with about twenty-five segments, the first about twice as broad as 

 long, the following gradually increasing in length, becoming squar- 

 ish on the fifth and following and slightly longer than broad 

 terminally ; the first three to five segments are slightly carinate and 

 rounded-prismatic; Pg about 10 mm. long, stouter than Pj but 

 similar to it, with about thirty segments; P3 3.5 mm. long, small, 

 weak, and slender, exceedingly slender in its distal half; P^ similar, 

 3 mm. long; P5 2 mm. long with ten segments not tapering so rapidly 

 as the preceding, and therefore appearing somewhat stouter; follov/- 

 ing pinnules similar, soon increasing slowly in length and slenderness; 

 distal pinnules very slender, 6 mm. long, with fifteen or sixteen seg- 

 ments. 



The color is deep violet, the cirri white. 



Type.—Csit. No. 27489, U.S.N.M., from station 5276. 



My studies upon the origin and significance of the nonmuscular 

 articulations in the crinoid arm "• have shown that the occurrence of 

 a true syzygy proximal to the syzygy between the third and fourth 

 brachials of the free undivided arm is a very anomalous condition. 

 Such a state of affairs has been supposed to exist in the comasterid 

 genera Comaster and Comatula, and in the Zygometridie. In the first 

 two genera I have been able to prove that the supposed syzygies are 

 in reality derived secondarily from the normal synarthries * and 

 have nothing to do with true syzygies at all. I had never seen any- 

 thing among the Zygometrida? which would warrant the statement 

 that the syzygy found between the two elements of their IBr series 

 is derived from a synarthry until the specimen just described came 

 to hand. In this the primitive synarthry is in process of transforma- 

 tion into a pseudo-syzygy through the development of radiating 

 ridges along the periphery of the joint face, which are apparently 

 extending inward toward the central canal. 



I now think that there can be no doubt that the "syzygy" between 

 the two elements of the IBr series in the Zygometridae is in reality 

 nothing more than a remarkably perfect pseudo-syzygy derived 

 secondarily from the synarthry, a condition called for by my inter- 

 pretation of the brachial homologies as explained in previous papers. 



aAmer. Nat., vol. 43, 1909, pp. 577-587; Proc. U. S. Nat. Mus., vol. 35, 1908, pp. 

 113-131. 

 bProc. Biol. Soc. Washington, vol. 22, pp. 173, 174. .,, 



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