OPHIURANS OF UNITED STATES NATIONAL MUSEUM. 89 



As we have about 0. pentacrinus only the description written in Danish by 

 by Liitken, of a very young specimen, unaccompanied with any figure, it will be 

 useful to again describe the species from the Albatross specimens, supplementing 

 the description with illustrations. 



The disk is rather tliick; its outline is pentagonal and it is stronly gexcavated 

 in the interradial spaces. The upper face is covered with dense, very short and 

 thin stumps, wliich are tliicker at their bases and terminated by a few very tlun 

 and divergent spinules; the latter are equal and often amount to three. These 

 stumps almost completely liide the outhnes of the plates from which they start 

 and which are very small. The radial shields are elongated and they generally 

 cause a fairly visible swelling, but their external region alone is apparent and they 

 are covered with stumps identical with the others over one-half or two-thirds of 

 their length. The two sliields of each pair are widely separated. 



The under face of the disk offers, in the interradial spaces, some plates wliich are 

 larger than on the upper face, cliiefly near the mouth shields, and with very distinct 

 outlines; these plates bear stumps wliich rapidly become smaller than on the upper 

 face and are reduced to the state of small, rough, and elongated granules before 

 they reach the mouth sldelds. 



The latter are small, twice wider than long, triangular, with an acute proximal 

 angle limited by two concave sides ai^ lateral angles now sharp, now slightly 

 rounded; the convex distal side sometimes offei-s at its middle a short and mdcned 

 little lobe, more or less apparent. The rather tliick adoral plates are bent in the 

 shape of a crescent, and tliinner near their external end, which does not separate 

 the mouth sliield from the first lateral brachial plate. The oral plates, of middle 

 size, are triangular. The oral papiUje, amounting to tliree, are conical and pointed, 

 and all have the same shape; the external one is sometimes a Uttle more obtuse 

 than the others at its end, but it is neither flattened nor widened. The single tooth 

 papilla is tliicker than the neigliboring ones. There is sometimes a fourth supple- 

 mentary oral papilla. Moreover, I observe that sometimes the first under brachial 

 plate carries, on each side, a Mttle papilla smaller than the others and advancmg 

 toward the tentacular mouth pore; tliis papilla is, moreover, often ill-shaped, or 

 even completely Jacking. 



The arms are very moniliform o^Ang to the enormous swelling which the lateral 

 brachial plates offer in their distal region; the middle part of the articles is, on the 

 contrary, very much narrowed. The upper bracldal plates, which are middle-sized, 

 are triangular with an acute proximal angle and a distal side vliich is almost straight 

 on the fii-st articles and afterwards becomes more and more convex; at first they 

 are wider than long and then they become ahnost as long as wide. These plates 

 strongly bulge out on then- dorsal face and are sei)arated by a very wade space, 

 which is almost as long as the plates themselves on the large specimens and becomes 

 still longer on the small ones. Sometimes the distal side is resolved into two short 

 sides which can even be sUghtly concave and join by an obtuse angle. 



The first under bi^chial plate is sometimes trapezoidal, longer than wide, and 

 narrow, with the proximal side wider than the distal side, which is rounded and has 

 converging lateral sides, sometimes simply triangular with a rounded distal apex. 



