448 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



not much shorter. The following pinnules become more slender and gradually in- 

 crease in length. The disk is 15 mm. in diameter, naked and moderately incised. The 

 ambulacra! grooves have lines of sacculi at their sides, which become very prominent 

 toward the margin of the disk, and give off branches to the first pair of pinnules. The 

 sacculi are large and abundant along the ambulacra of both arms and pinnules. The 

 color in alcohol is reddish white, with dark-red lines at the articulations; the ventral 

 perisome is gray or purplish gray. 



Carpenter said that the pinnules of the second pair (P 2 and P b ) in this unique 

 specimen of Antedon marginata terminate so abruptly that they seem to have been 

 broken off by some accident and not completely repaired. The diameter of the seg- 

 ments suddenly decreases, and there are from one to four quite small segments at the 

 end of a large and stout one which is considerably longer than broad. He noted further 

 that the disk of this specimen is remarkable for the abundance of sacculi upon it. 

 There is a line of them along each side of the ten secondary ambulacra, and branches 

 proceed direct from these lines to the primary pinnules, thus marking the course of 

 their water vessels which, however, have no tentacular extensions. 



I examined this specimen at the British Museum in 1910. P 3 , though not espe- 

 cially enlarged and about the length of the succeeding pinnules, is more of the character 

 of P 2 and is somewhat stouter than those succeeding; it is flagellate distally. P 2 curves 

 strongly backward and is not erect as is usual in S. protectus. At that time I regarded 

 marginata as possibly a form of protectus ("monacantha"), though probably distinct. 

 Dr. Torsten Gisle"n examined this specimen in 1925. He identified it as monacantha 

 (=protectus). He wrote that only P 2 is stiffened, Carpenter's description being not 

 quite correct in this particular. 



Two of the specimens from Port Galera, Mindoro, are large with 16 arms. 



In one of the specimens from Santa Cruz Island, Zamboanga, there are 20 arms 

 80 mm. long. Ten IIBr 2 series are present. The cirri are XXVII, 19-20, from 16 to 

 18 mm. long. P 2 is 13 mm. long and is composed of 16 segments. This pinnule is 

 markedly longer and stouter on the outer arms of each postradial series than on the 

 inner, the corresponding pinnule on the inner arms being of the same size as P s , or 

 somewhat smaller. Another specimen has 20 arms 90 mm. long. A third specimen 

 has 14 arms 80 mm. long; P 2 is 14 mm. long with 15 segments. A fourth specimen has 

 13 arms 80 mm. long; P 2 is 10 mm. long with 12 segments. There are eight additional 

 specimens. 



The example from Siboga station 96 has 17 arms and is undergoing adolescent 

 autotomy. P 2 has 9 segments, of which the first two are about as long as broad and 

 the third is twice as long as broad. 



In the two specimens from Mortlock Island described by Hartlaub the centro- 

 dorsal is moderately thick, convex, with convex sides ; the bare dorsal pole is small and 

 pitted. The cirrus sockets are arranged in three irregular rows. The cirri are XXX- 

 XXXV, about 20. They are laterally compressed. From the fifth onward the 

 segments are longer than broad, toward the end of the cirri gradually becoming shorter 

 again. They bear dorsally neither tubercles nor spines. Seen from above they are 

 somewhat hourglass-shaped, their distal end being thickened and the distal edge 

 being produced, especially on the ventral side. The surface of the cirri is thus un- 

 even. The radials are only slightly or not at all visible. The IBr, are entirely free 





