104 BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



of the said distal edge there is a little lobe which is not very conspicuous. The 

 adoral plates are elongated, three times longer than wide, with parallel and slightly 

 incurvate sides; they are somewhat narrower inwardly and outwardly and they 

 do not separate the mouth shields from the first lateral brachial plate. The oral 

 plates are rather small and triangular. The oral papillffi, amounting to three on 

 each side, are flattened, lanceolate, with a more or less blunt point; the external 

 papilla is a Uttle wider than the others. The odd terminal papilla is a little more 

 developed than the next ones. The surface of these papillas is covered with very 

 fine rugosities. 



The first upper brachial plate is quadrangidar and extremely short. The 

 second is longer and much more developed but it still remains quadrangular with 

 a very wide and convex distal side and divergent lateral sides. The following plates 

 are rather large, triangular, with an acute proximal angle, a convex distal side and 

 divergent lateral sides. Some globules, analogous to those of the upper face of the 

 disk, appear on the first bracHal plates; the first plate shows four or five such 

 granules set in a row, generally on its distal margin ; the second plate also displays, 

 on its distal margin, a little row of three such globules; lastly, the seven or eight 

 succeeding plates have each, on the middle of their distal margin, a single globule 

 which is somewhat more elongated than the preceding ones. These globules seem 

 to fall off easily and they are lacking on several plates; on one of the arms, however, 

 I find them very regularly preserved up to and including the seventh plate; beyond 

 it, they are always absent and I find no scar indicating their presence. 



The fu-st under brachial plate, fairly large, is quadrangular, ^\'ith a widened 

 and almost straight proximal side, obhque lateral sides meeting, by means of 

 rounded angles, the distal side, which is narrow and also rounded. The succeeding 

 plates are fairly large and pentagonal, with a very obtuse proximal angle, straight 

 lateral sides, and a very convex distal side, which often displays, in its middle and 

 on the first plate, a small notch, more or less conspicuous. The second and third 

 plates are a little wider than long; beyond them the plates become as wide as long, 

 and finally a little longer than wide. They are separated from the second one. 



Each lateral plate, fairly protruding, carries on its distal side five spines, the 

 length of which increases from the fii'st ventral, which is equal to the article, to the 

 fourth, equal to one and a half articles; the fifth spine is somewhat shorter. These 

 spines are cylindrical, fairly pointed, and they bear dense and sharp asperities, 

 some of which even rise to more conspicuous denticulations, which, however, are 

 generally few in number. 



The tentacular scale, always single, is very large, widened and lanceolate, and 

 its svirface is rough; its length almost reaches that of the corresponding brachial 

 plate. 



Connections and differences. — 0. americana is very near 0. globulifera (Koehler), 

 which I have dredged on board the Caudan in the Bay of Biscay; it differs from it, 

 first by the characters of the globules of the upper face of the disk, which are rounded, 

 transparent, and completely smooth in 0. globulifera. Moreover, the globules are 

 completely lackmg on the upper brachial plates in tliis latter species. The tentac- 

 ular scale is stronger in 0. americana, and the outlines of the mouth pieces are 

 somewhat different in the two species. 



