6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 9I 



the jaw plate where it adjoins the adoral shield. The third is inter- 

 mediate between the second and the other four, which are much 

 narrower and pointed, those on either side of the apex of the mouth 

 angle being the longest and most robust. There are four rather long, 

 narrow, lanceolate, pointed teeth, and above these a single similar, 

 but narrower, tooth papilla, almost on a level with the adjacent mouth 

 papillae, which it resembles except that it is longer and stouter. 



The second and third under arm plates are slightly broader than 

 long with the distal edge gently concave, the distal angles broadly 

 rounded, and the lateral edges excavated by the oval tentacle pores, 

 and the proximal angles truncated by the side arm plates. Distally the 

 under arm plates become narrower with slightly convex distal ends 

 sometimes with a slight median depression or notch, and the trunca- 

 tion of their proximal angles rapidly increases until after about the 

 fifteenth-seventeenth they end proximally in a sharp or slightly trun- 

 cated angle, the side arm plates almost or quite meeting beneath them, 

 and are half again as long as their distal edge, just beneath the outer 

 ends of which the circular tentacle pores lie. Further out they become 

 narrowly fan-shaped with a long narrow proximal angle beyond which 

 the sides are excavated by the tentacle pores, and by the meeting of 

 the side arm plates beneath them become separated from each other 

 for a distance equal to about half their length. The distal edge of the 

 under arm plates is convex, that of the larger proximal ones being 

 more or less markedly biconvex with a median sharp or rounded 

 notch. The earlier under arm plates, up to about the twentieth, have 

 a fine median longitudinal line that distally becomes obscure. The 

 surface of the plates is highly polished and glassy, and is finely sculp- 

 tured with transverse lines. 



The second and third upper arm plates are trapezoidal, much 

 broader than long, the fourth is about as long as the distal width, and 

 those following gradually decrease in width, at about the seventeenth 

 becoming narrowly fan-shaped with a very acute proximal angle, and 

 about twice as long as the distal width. Distally they become exceed- 

 ingly small, and are widely separated by the side arm plates. The 

 aboral surface of the arm is sharply and conspicuously carinate, and 

 the large proximal upper arm plates tend to split into two parts along 

 the carinate midline. 



The lateral edges of the arm are more or less sharply carinate, the 

 carinate ridge being sometimes more or less finely spinous. The 

 lateral and aboral carination is accentuated by the slight excavation 

 or depression of the aboral portion of the large side arm plates. The 



