90 BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



The second plate, which is already separated from the preceding one by the lateral 

 plates, is very large, triangular, with a proximal angle limited by two almost straight 

 sides, and a strongly convex distal side ; it always remains wider than long. The 

 proximal angle becomes more and more obtuse on the following plates, which are 

 pentagonal, with two small lateral sides and a distal side wliich is always strongly 

 convex. All these plates always remain fairly large, wider than long, and the space 

 which separates them is larger as the examples are smaller. I have found in Liitken's 

 type the confirmation of the fact that the under brachial plates, however small 

 they may be, always remain wider than long. 



The lateral brachial plates bear on the whole length of their distal side, which 

 is thickened and widened, at least seven spines on the first articles and sometimes 

 eight in the largest specimens. The first three spines are not very large; they are 

 almost equal and the third one reaches about the length of the article. These three 

 spines are rather thick, cylindrical, with an obtuse end, and they show extremely 

 fine and dense denticulations. Afterwards the length of the spines rapidly in- 

 creases and the two or three last dorsal ones become extremely long, slender, pointed, 

 transparent, with stronger and widely spaced denticulations, the number and size 

 of which varies greatly. The length of the dorsal spines exceeds three articles at 

 the bases of the arms, then it progressively decreases and finally does not exceed 

 the article in the second half of the arm. The number of spines decreases beyond 

 the first articles and remains five in number on the larger part of the length of the 

 arms. On the first articles, the two rows are very approximate dorsally. 



The tentacular scale is small, spiniform, pointed, rough, or even provided with 

 small asperities. 



0. pentacrinus does not seem to acquire great dimensions and the diameter of 

 the disk ranges between 3 and 5.5 mm. 



0. pentacrinus has undoubtedly been mistaken by Lyman for another species 

 in which the oral papilla is wide and flattened, a character which 0. pentacrinus 

 does not show in Liitken's type. It is likely that the specimens gathered by the 

 Blake and referred to by Lyman in 1883 under the name of 0. meridionalis Lyman = 

 O. pentacrinus Liitken, included a mixture of the two forms ; these specimens ought 

 to be sorted out. In any case, Lyman designated under the name of 0. pentacrinus, 

 a term which according to him was the synonym of 0. meridionalis, some specimens 

 which had their external oral papilla widened and flattened, since three specimens 

 from the Blake which certainly have been determined by him, were sent to the 

 Jardin des Plantes under the name of 0. pentacrinus. Consequently, if after making 

 the comparison with Liitken's type, we keep the name of 0. pentacrinus for an 

 Opniacantha the external oral papilla of which is not widened but preserves the 

 same shape as the other two, we may give the name of 0. meridionalis to the neigh- 

 boring species which Lyman had confused with it and in which the said papilla is 

 widened and flattened. Now, I find among the Ophiurans gathered by the Albatross 

 some specimens which offer precisely the same character, and I shall describe them 

 further under the name of 0. meridionalis. 



The characters of 0. pentacrinus do not seem to me to have been better dis- 

 tinguished by Verrill; what is more, I notice a contradiction in the two passages 



