OPHIUKANS OF UNITED STATES NATIONAL MUSEUM. 113 



their free edges they each carry five conical and pointed papillae ; the most external 

 ones are thin, then their width slightly increases up to the last one which becomes 

 rather wide and contiguous with the median tooth papilla; these five papillae form 

 an uninterrupted row. There are no other tooth papillae besides the odd median 

 one. Off the next papilla, and isolated from it by a varying interval, there is 

 another papilla which is inserted near the juncture of the oral and adoral plates, 

 and which consequently corresponds to the proximal side of the tentacular mouth 

 pore; a little further appears a second similar papilla which is also inserted on the 

 adoral plate, but which corresponds to the middle of the tentacular mouth pore. 

 These two papilla? are more elongated than the others and they are almost spiniform, 

 especially the latter. 



The upper brachial plates are rather small, triangular, with a convex distal 

 edge and a fairly open proximal angle which is often slightly rounded; they are 

 almost as long as wide. These plates are separated from the bases of the 

 arms by an interval which progressively increases and which, beyond the first half 

 of the arms, exceeds the length of the said plates. 



The first brachial middle-sized under plate is trapezoidal, with a wider proximal 

 side, a fairly narrow distal side and divergent lateral sides; it is already separated 

 from the second one by a narrow interval. The succeeding plates are pentagonal 

 with a very obtuse proximal angle, which, beyond the disk, is so widely open that 

 it almost reaches 180; the lateral sides are divergent and widely excavated by the 

 tentacular pores: they join by acute angles the distal side which is very wide and 

 strongly convex and has in its middle a very conspicuous notch. These plates 

 are much longer than wide and they remain separated on the whole length of the 

 arms by an interval which by degrees grows longer, without, however, becoming as 

 important as on the upper face. 



The little protruding side plates bear four fine, cylindrical, elongated, and 

 pointed spines which are more or less divergent and set apart from the arm; the 

 length of these spines increases from the first ventral which is a little longer than 

 half the article to the last dorsal which is almost equal to one and a half articles. 



The tentacular scales of the brachial pores show the characteristic arrangement 

 of the genus Ophiotrema, that is to say, they appear in the shape of very small, 

 fine, and pointed spines arranged on the proximal edge and on the internal or 

 radial edge of each pore; these spines, amounting to five or six on each pore, are 

 seldom preserved integrally; they have not always the same length, and those of the 

 proximal side of the pore are sometimes a little longer than the others. 



Connections and differences. 0. gracilis evidently belongs to the genus 

 Ophiotrema as I have established it. It differs from the single known species, 

 0. alberti, in having slender arms and only four brachial spines which are thin and 

 elongated, much longer and finer than in 0. alberti where they amount to five and 

 always remain applied against the lateral faces of the arms. The upper brachial 

 plates are narrower, smaller, and more widely separated; the under brachial 

 plates are longer in 0. gracilis. The tentacular mouth pore is provided with only 

 two papillae which are elongated, cylindrical, and pointed, rather spiniform, instead 

 of three short and oval papillae such as exist in 0. alberti. The small spines of 



