OPHIURANS OF UNITED STATES NATIONAL MUSEUM. 15 



Beyond that the plates, wliich up to that point were separated only by the trans- 

 verse furrow which I have mentioned above, go farther and farther apart from each 

 other; they become at first pentagonal |and as long as wide, and soon assume a 

 triangular shape with a very convex distal margin, and at the same time become 

 wider than long. It must be noticed that the first under plates have granules just 

 like the other plates of the body, but about the eighth plate these granules begin to 

 be arranged in regular transverse sets which will form pretty well marked striae on 

 the surface of the next plates. A like structure appears only to a very small extent, 

 or is even completely lacking, on the lateral plates. 



Tlio lateral plates are broadly develojx?d and take up an important part of the 

 upper and under faces of the arms; their surfaces are covered with granules, which 

 disappear only at the extremities of the arms. On their distal margin there are 

 generally three short, papilUform, and sharp spines, the dorsal s]Hne being a little 

 isolated from the other two. On some articles of one of the arms I exceptionally 

 find four spines which are separated by equal intervals. 



The tentacular pores of the first pair open ^\'idcly in the mouth, and they 

 gencrallj' carry five scales on each margin; these scales are small, tnmcated, very 

 closely put together or even somewhat jointed. Tlie pores of the second pair have 

 four or five scales on the proximal or external margin and four on the opposite 

 margin, the latter being less developed than the proximal ones. A like arrangement 

 is observed on the pores of the third and of the fourth pair. On the pores of the 

 fifth and sixth pairs the proximal margin carries four scales and the distal margin 

 has but two small ones. On the following pores these distal scales rapiilly dis- 

 appear, but of the proximal scales there remain three, a number wliich is persistently 

 found on almost the wiiole length of the arms; but the scales become smaller, short, 

 and conical. 



The color of the specimens in alcohol is grayish-wliitc. 



Resemblances and differences. — 0. coronata is evidently closely alUed to 0. conr 

 vexa, although distinct from it. I tliink the two should be separated. We have 

 seen that Lyman had already attempted to do so. The six primaiy plates are 

 largely developed, and they take up on the upper face of the disk a comparatively 

 larger space than in 0. convexa, so as to leave room for only a single interradial 

 plate, a very large one, larger even than in 0. convexa. Tlie radial shielils are rela- 

 tively small and more reduced than in the latter species. The radial papillaj are 

 extremely narrow, cylindrical, elongated, pointed, numerous, and closelj-put together, 

 and they completely differ from those wliich are known to exist in 0. convexa, these 

 latter being rather low and rectangular, as I indicated in 1909 (09, p. 149). 



Tlie arms are far less carinated than in 0. convexa. Tlie upper brachial plates 

 are quadrangular on the first articles only and rapidly become triangular, while in 

 0. convexa they remain quadrangular on more than half of the lengtli of the arms, 

 and become triangular only beyond that point, although they remain as long as wide 

 or even a little longer than wide. On the under face the arms are more widened 

 at their base, consequently the interradial spaces are narrower than in 0. convexa 

 and the mouth sliields themselves are also narrower. I>3-man had observed that 

 in some specimens of the Blal-e these shields covered the whole under face of the 

 disk inwardly of the genital plates; such is not the case in ni}' two examples, which 



