2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 9I 



radial shields from the arm base. In the interradial line a row of 

 plates, of approximately the same width as the radial rows, runs 

 from the central rosette to the edge of the disk. This row consists of 

 three plates, first a six-sided plate about half again as long as broad, 

 with the two distal outer sides converging to the rather narrow distal 

 edge on which rests a long plate, more than twice as long as broad, 

 with very slightly converging sides, which is followed by a much 

 shorter, but slightly broader, plate, situated on the edge of the disk. 

 On the outer edges of the radially placed plates and between the 

 bases of the radial and interradial rows are one or two small rounded- 

 triangular plates. The surface of all the plates on the al^actinal sur- 

 face of the disk is studded with small, regular, and closely set tubercles, 

 those on the radial shields being rather larger and more widely spaced 

 than those on the other plates. 



On the oral surface the mouth shields are small, longer than broad, 

 the outer half with the sides parallel, the inner half with the sides 

 forming an angle of about 60°. The adoral shields are large, with 

 about the same area as the mouth shields, wedge-shaped with straight 

 sides, the outer end being about twice as broad as the inner. The jaw 

 plates are low triangles bearing on their longest (outer) side a row 

 of five blunt mouth papillae which slowly and gradually diminish in 

 k-ngth and width toward the apex, where an unpaired triangular 

 papilla lies on the suture between the jaw plates. The genital slits 

 run from the pointed ventral ends of the bands of papillae that sepa- 

 rate the radial shields from the arm bases, beneath the outer sides of 

 the second side arm plates, to the obtuse angle in the lateral borders 

 of the mouth shields. They are bordered with 12 to 14 flattened 

 papillae with broadly rounded ends. Beyond the mouth shields is a 

 large plate of about the same width, about twice as broad as long, 

 which is often divided into two small plates. Beyond this is a larger 

 rounded plate on the edge of the disk, between the upper portion of 

 which and the large genital plate on either side is a single rounded and 

 protuberant plate, with another similar but smaller one just beyond 

 and nearer the interradial line. 



There are three pairs of tentacle pores, each with a large rounded 

 tentacle scale situated on the side arm plate. 



The first side arm plate beyond the disk bears two short arm spines 

 rather close together near the middle of its outer edge. The second 

 bears one spine above the middle and two, close together, below, or 

 only the latter, and those following to the eighth or tenth bear two 

 short peglike spines close together below the middle. Beyond the 

 eighth to tenth side arm plate the upper arm spine becomes trans- 



