OPHIUEANS OF UNITED STATES NATIONAL MUSEUM. 85 



Verrill states that the tentacular scale is "flattened, small, tapered, subacute"; 

 the form which I observe on my own specimen is a little different. Indeed, this 

 scale, of middle size, appears flattened, elongated, fairly wide, and it always keeps 

 the same width throughout its whole length, or even becomes a little wider in its 

 distal part to end with a rounded edge; its surface is very rough. 



All the specimens from stations 2105 and 2678 are smaller than the foregoing 

 one, and display a few differences which are evidently due to their age. The radial 

 ribs are distinct on only a few specimens, the diameter of the disk of which ranges 

 between 5 and 8 mm. ; in the two largest ones, the upper face of the disk displays 

 corrugations which have very likely caused the relief of the ribs to disappear. The 

 upper brachial plates are generally separated from the base of the arms. The 

 under brachial plates are always wider than long at the base of the arms, but they 

 afterwards become as wide as long, and they even become a little longer than wide 

 at the ends of the arms. The mouth shields often have their side angles sharper 

 than those of the specimen from station 2573, but they generally remain rounded; 

 the oral papillae preserve the usual arrangement. On the two larger specimens 

 from station 2105, the tentacular scales of the first brachial articles are thinner 

 and sharper than on the articles which succeed the disk, where they take the shape 

 which I have reported above; but on the smaller samples, the form which I observe 

 is nearer to the one indicated by Verrill, that is to say, the scales are thinner and 

 subacute, sometimes a little lanceolate, but always fairly long. 



Verrill connected 0. fraterna with 0. bidentata, the latter offering certainly a 

 great analogy with the former. It will, however, always be possible to distinguish 

 the first from the second species; by the form of the external oral papilla which is 

 not widened and offers the same shape as the other two in 0. fraterna, where it 

 is elongated, cylindrical, and almost spiniform; by the brachial spines being rougher; 

 by the small stumps of the upper face of the disk being thinner and ending in a 

 bunch of notably stronger spinules. The mouth shields and the adoral plates have 

 almost the same shape in both species. 



But it is not to 0. bidentata that 0. fraterna is most closely allied; it is 

 undoubtedly nearer 0. aculeata Verrill, and the comparison with the latter is all 

 the more necessary because I have found both species in the lot of Ophiurans which 

 came from station 2105. All the 0. fraterna of that lot being smaller than the 

 0. aculeata, the question might be asked whether the former were not simply 

 the young of the second species. Above all, the shape of the external oral papilla 

 will always allow 0. fraterna to be distinguished from 0. aculeata. In fact, in all 

 the 0. fraterna observed by me, in which the diameter of the disk varies from 3 to 

 9.5 mm., this papilla always remains identical with the other two, and although I 

 have observed no specimen of 0. aculeata less than 12 mm. in diameter, it is 

 not admissible that the shape of that papilla begins to alter only when the disk of 

 the Ophiuran has reached a diameter superior to 9 mm., and that it only then takes 

 the strikingly widened shape which it displays in 0. aculeata, the diameter of which 

 is 12 mm. or more. If we compare some specimens of 0. fraterna, such as the one 

 from Georges Bank, the disk of which is 10 mm., with some 0. aculeata, such as the 

 one represented on plate 1 1 , figures 1 and 2, the diameter of the disk of which is about 



