g 2 NATURAL HISTORY BULLETIN. 



ninth or tenth joint there are two small thorny ones, and 

 farther out only one, which is very slender and rough. 



The size of the tentacle-pores also decreases rapidly from 

 the basal joints distally, so that even on the middle of the 

 arm it becomes minute. 



Along the basal half of the arm. beneath, there is a shallow, 

 median groove, which increases in depth proximally; it is due 

 to the concave form of the under arm-plates. The under 

 arm-plates beyond the basal, are short, but transversely very 

 wide, with the lateral angles extending far out between the 

 side plates and up on the sides of the arms; the distal edge is 

 distinctly three-lobed, the lobes being broadly rounded, the 

 median a little more prominent than the lateral; the proximal 

 end has a very obtuse median angle. They are slightly sep- 

 arated by the side arm-plates; on the middle of each under 

 plate there is a slightly raised, small, rough elevation. The 

 side arm-plates are short, but high and rather prominent; 

 they meet both above and below. 



Arm-spines seven or eight on the second and third joints 

 beyond the disk. They increase regularly in length from 

 the lowest, which are small and slender, to the two upper 

 ones, which are large and long, or about as long as four arm- 

 joints. They are slender, tapered, terete, translucent, and 

 covered with small rough points on all sides. 



The rows of spines do not approach very closely on the 

 upper side 'of the arm, owing to the width of the arm-plates. 



The upper arm-plates are strongly arched, rather thick 

 and swollen, rough, with a transverse row of small verruca; 

 on a low ridge near the distal edge. These plates, except a 

 few basal ones, are transversely subrhombic, or rudely ellip- 

 tical, with the inner end obtusely angulated and the outer end 

 broadly convex, and often obtusely angulated medially. They 

 are much wider than long, and are separated by deep, narrow 

 grooves in which the side plates meet. 



The first four or five dorsal plates are smaller and narrow- 



