134 PROCEEDINGS OF THE ACADEMY OP [1886. 



ring, is the azygous plate, which has not only the form but gene- 

 ral appearance of the four radials. It supports upon its truncate 

 upper side the fifth radial, that of the right posterior my. The 

 latter, which resembles in form a large bifurcating plate, sup- 

 ports upon its right upper side the brachials, and toward the 

 left the first plate of the anal tube, being thus a radial, but partW 

 with interradial functions. The radials in all five rays are fol- 

 lowed by five to six brachials, the upper one bifurcating, the 

 others quadrangular, all wider than long, and those of adjoining 

 rays meeting laterall3^ Tiiese are succeeded by the regular arm 

 plates. 



Arms long, gradually tapering to the tips ; bifurcating at regu- 

 lar intervals, and most of their branches bifurcating once or 

 twice again ; each division extending to the general height of the 

 arms. Arm joints quadrangular, resembling those of the brachi- 

 als, but somewhat narrower. 



The ventral sac, at its posterior side, consists of a single row 

 of rather large and strong plates, extending up to the full length 

 of the sac, and forming all the way up a keel-like projection. 

 In general appearance, these plates, which rest against the sloping 

 side of a radial, resemble the brachials and arm plates, although 

 they are somewhat higher and not as wide. Both sides of the 

 ridge-like projection are indented for the reception of other plates. 

 At each side there are two pieces connected to each median plate, 

 one abutting against the middle part, and the other placed oppo- 

 site the suture. These plates are A^ery short and wide, longitu- 

 dinally arranged ; they are curved so as to form a deep transverse 

 groove, their lower sides turned up and forming a transverse 

 ridge. The plates do not meet horizontally, but have a narrow 

 open space at the top of the ridge, which in perfect specimens is 

 covered by a row of minute pieces, apparently with a pore or 

 small opening at the place of juncture with the larger plates. 

 The sac is composed of five rows of these plates, which are con- 

 nected laterally by a straight suture all the way up. 



Column strong, sharply pentagonal, its angles in a line with 

 the radial plates. 



We add the following species to our former list: 



ISSy. locrinus trentonensis Walcott, Adv. sheets of 35th Rep. N. Y. St. Cab. Nat. 

 Hist., p. 4, PI. 17, tigs. 7, 8. Trenton limest. Trenton Falls, N. Y. 



