74 Bulletin, Vanderbilt Marine Museum, Vol. IV 



pedicellariae ; as many as nine are found in a single cluster of pores. 

 The madreporic plate is large, situated on one side of the ray, about 

 half an inch from the center of the disk, and is irregularly sub- 

 circular, with its upper surface broken into many irregular radiating 

 ridges, separated by equivalent grooves. The superomarginal plates 

 which form the greater part of the border are about a half inch deep 

 in the median two-thirds of each arc, slightly less so towards the tips 

 of the raj r s. There are 15 to 16 plates on each of the five arcs, the 

 median seven or eight being oblong, much broader than long, while 

 the outer four of each series are nearly square, the outermost one 

 being swollen. There is a stout, conical spine on each plate near or 

 slightly above the middle of the plate. The inferomarginal plates 

 number twenty to the arc, and are near the ventral surface in the 

 median region of the series, but tend to form more of the margin 

 toward each end. Each plate bears a stout, conical spine similar to 

 but larger than those of the actinal surface. The median plates of 

 each series are the smaller, squarish; the outer one four or five times 

 longer than broad, except the outermost one which is smaller, trian- 

 gular and well up on the tip of the ray. The actinal surface is covered 

 by numerous low, rounded, tabular paxillae that become finer and 

 closer toward the marginal plates, both series of which they com- 

 pletely cover. On the actinal surface rather regularly spaced among 

 the paxillae are larger, short, blunt, conical spines, the smaller spines 

 of the series occupjdng the outer portion of each interradial space, 

 while near the center the spines become distinctly larger. Scattered 

 among the actinal paxillae are many small, stout, oblong pedicellariae, 

 similar to those on the actinal surface. The interambulacral plates 

 near the mouth bear seven or eight blunt, flattish, slender spines in a 

 single row, the two apical spines the longest. Outside of these there 

 is a row of very stout, rounded spines with blunt tips, spaced one 

 opposite each cluster of the interambulacral spines, those near the 

 jaw angle being the largest, the series diminishing in size toward the 

 end of the rays, where they become small and more acuminate. The 

 ambulacral furrows are narrow and turn upward at the end of the 

 rays and terminate between the swollen upper plates. 

 References: Pentaceros (Nidorellia) armatus Gray, Ann. Mag. Nat. 



Hist., vol. VI, p. 276, 1840. 

 Orcaster armatus Muller and Troschel, System der Asteriden, p. 52, 



1842. 

 Goniodiscus armatus Lutken, Vidensk. Meddel., p. 59, 1859. 



