I0 NATURAL HISTORY BULLETIN. 



The oral side of the disk has, on each interradial area, four 

 large, submarginal plates, of which the two median are larger, 

 and usually oblong; between these and the oral shields there 

 are usually five or six irregular and unequal plates. 



The oral shields are large, oblong-oval or shield-shaped, 

 longer than broad, the sides nearly parallel, indented, and the 

 outer ends rounded, while the inner margins form a sharp 

 angle. Lateral oral plates, large, elongated, curved, thick- 

 ened and in contact proximally at their narrow ends. 



Oral papilla; rather numerous, five to seven on each bor- 

 der; the next to the outer one is largest, flat, with the edge 

 rounded; the others are mostly small, conical, and acute. Be- 

 yond the middle of the arm they become more triangular, 

 with a slight median prominence on the outer end. 



The under arm-plates are large, shield-shaped, widest 

 distally, with the lateral edges incurved; proximal end round- 

 ed or truncate, and the outer end broadly rounded. On the 

 basal joints they become wider and shorter, with the prox- 

 imal end much narrower than the distal. Tentacle-scales on 

 the proximal joints, two, rather large, flat, broad ovate; farth- 

 er out there are often three, of which one is very small. 



Arm-spines three (rarely four), small, conical, near to- 

 gether, well down on the sides of the arm; the upper one is 

 usually a little smaller than the others. Upper arm-plates, 

 except a few close to the base of the proximal half of the arm, 

 broad-trapezoidal or triangular, with the outer lateral corn- 

 ers prominent and acute; the outer edge is broadly round- 

 ed; the sides nearly straight, or a little incurved, and strongly 

 divergent; the inner end, <>n the proximal ones, is narrow and 

 truncated; those beyond the middle of the arm are triangular. 



The three basal plates are small and very short; the fourth 

 is crescent-shaped; the fifth is much wider than long; farther 

 out the ratio of the length to the breadth increases. 



The diameter of the disk of the largest specimen is 16 mm.; 

 length of longest arm, which is broken at the tip, 34 mm. 



