44 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



acute proximal angle, and they are then longer than broad. These 

 plates are almost in contact throughout the length of the arm, but 

 in the terminal portion they end by being separated by an extremely 

 narrow interval occupied by the side arm plates. 



The side arm plates project only slightly. They bear on their sides 

 as well as on their ventral border a series of spines numbering five 

 at the base of the arms ; this figure falls to four at some distance from 

 the disk. These spines are shorter than the segment, and are ap- 

 pressed against the lateral surface of the arms ; they are rather thick, 

 cylindrical, and rugose. The little asperities which they show become 

 more marked toward their tips, which are rounded, and they then 

 form short and extremely small spinules. These spines are all sub- 

 equal and a little shorter than the segment. In the distal half of the 

 arm their number falls to three, then to two, and finally they dis- 

 appear entirely. On the first arm segments the insertion of the first- 

 dorsal spine is very close to the external angle of the corresponding 

 upper arm plate, then on the following segments it gradually draws 

 away in such a manner as to form on the anterior border of each 

 side arm plate, a rather broad area bare of spines. This area is 

 occupied by a row of little hooks, which at first are two or three in 

 number, but later as many as six. These hooks (figs. 4, 7) formed 

 of an entirely transparent substance, end in a recurved and pointed 

 tip below which are one or two teeth. They are inserted on a little 

 elevation, in the form of a rounded nipple, of the free border of 

 the side arm plate (fig. 8). These nipples are very conspicuous and 

 they indicate the places where the hooks originally stood (fig. 5) 

 after they have been torn off. The hooks measure from 0.5 mm. to 

 0.6 mm. in length at the base of the arms, gradually decreasing in 

 length distally ; those which I have represented in figure 4 in plate 7, 

 and which are from the terminal third of an arm, are not more than 

 0.2 mm. in length ; the broadened basal part, provided with numerous 

 orifices and composed of a compact substance, is rather short, almost 

 as long as broad, and its length equals almost a third of the total 

 length of the hook. The hook proper, which is formed of an abso- 

 lutely transparent substance, terminates in a very long tooth, which 

 is recurved, so as to form a right angle with the principal portion 

 of the hook, which it almost equals in length. Behind this terminal 

 tooth there are three or four other teeth, which are very much smaller 

 and diminish rapidly in size toward the base, near which there 

 appears again a last tooth larger than the preceding. In the proximal 

 region the hyaline part of the tooth shows from three to five succes- 

 sive rounded or oval orifices, which are often regularly arranged one 

 after the other. 



The tentacular pores each have two unequal scales ; the external is 

 very large and broad, rounded, almost as long as broad, while the 



