OPHIUBANS OF UNITED STATES NATIONAL MUSEUM. 75 



invisible. Vcrrill has pointed out that these stumps were "smaller, longer, and 

 more slender than in 0. bidentata," with which he connects 0. aculeata. 



The under face of the disk, in the interratlial spaces, is covered with stumps 

 which are analogous to those of the upper face but shorter, a little tliicker, less 

 dense, and allowing the outlines of the plates to be seen ; they extend as far as 

 the mouth shields. The genital slits are elongated and narrow. 



The mouth shields are rather small and much wider than long, triangular or 

 lozenge-shaped, with an obtuse proximal angle limited by two straight sides which 

 meet, by a rounded angle, the distal side, which is more or less convex; tlie latter 

 is usually parted into two sides, united by a rounded and protrudhig angle. 

 According to the more or less protruding character of this angle, the shield is either 

 triangular or lozenge-shaped. The adoral plates are elongated, narrow, three or 

 four times longer than wide, with [almost parallel edges; they send outwardly a 

 rather narrow blade which separates the moutli sliield from the first lateral 

 brachial plate. The oral plates are fairly lai^c, liigh, and triangular. The oral 

 papUlae, as a rule, are three on each side; the external one is flattened and very 

 much widened, chiefly at its base, but it often has an end which is tliinner and 

 terminates in an obtuse point. Such is, at least, the arrangement which I observe 

 on the example from station 2725 and which I also find on one of the specimens from 

 station 2105, the diameter of the disk of which reaches 14 mm. On the others the 

 arrangement of the oral papillas remams regular at least on certain sides of the 

 oral angles, but it is more or less altered on other sides. Verrill has pointed 

 out that "sometimes an additional smaller one [oral papilla] stands out of line, 

 behind those in the regular row." On the specimen from which I made my descrip- 

 tion (pi. 11, fig. 2), one of the oral plates carries a supplemental papilla, so that 

 there are four in all on that side, the external one always kee])ing the usual widened 

 form, and the other three being conical and equal; on anotlier sitle I notice a little 

 papilla which lies near the second normal one; the other eiglit sides present the usual 

 arrangement. On two other examples there is on two sides a little supplemental 

 papilla located between the most external and the preceding one. Finally, in others, 

 one may find, instead of a single and odd dental ])apilla, two or three larger or smaller 

 papillae which, moreover, remain irregular in shape and number in the same speci- 

 men. In the lai^est specimen two dental papillae are generally to be noticed, 

 except on one of the jaws, and besides, sometimes there is a supplemental oral 

 papilla on the sides, and therefore here is another example worth pointing out of 

 the variations which the oral and dental papillae of the Ophiacanthida; may offer. 

 I beg to call attention to these differences owing to the importance given b}- Verrill, 

 when he classified the Opiiiacanthidae, to the arrangement of these papillae ; in fact 

 if we strictly observed the diagnoses of the genera or subgenera wliich he established, 

 certain specimens from station 2105 ought to be classified in the genus Op/iiaca7i<^a, 

 s. str., others in the genus OpMentodia, and a few might be placed indifferently 

 in one genus or the other, according to which mouth angle one considers. 



The arms are long, fairly wide, and not at all moruliform, although the lateral 

 bracliial plates are fairly protruding; they gradually get narrower up to their ends 

 and the articles are short. The upper brachial i)lates are fairly large, triangular, 

 with an acute proximal angle, and a wide and convex distal side; they are wider than 



