MUSEUM OF COMPARATIVE ZOOLOGY. 323 



lines between them ; there are seventeen to each angle, of which the 

 outer one is tooth-like and minute, and may be partially detached from 

 the rest ; the innermost, odd one is diamond-shaped, and lies immediately 

 under the teeth ; the others are squarish. Teeth four, Hat, pointed, nar- 

 row ; sometimes not placed regularly over each other. Mouth-shields 

 small, of a truncated diamond shape, the truncation directed outward ; 

 length to breadth .8 : .(J. Side mouth-shields broader without than within, 

 where they meet, extending outwards beyond the mouth-shield, and join- 

 ing the first side arm-plate; length 1.2 mm. Disk smooth above, and below, 

 and covered with a close mosaic of rounded scales, so intimately soldered 

 that their outlines are indistinct. Radial shields blunt pear-seed shaped, 

 widely separated by a group of small disk scales ; length to breadth 

 1.8 : 1.2; they swell a little above the level of the others, and their 

 surface, under the microscope, is composed of smooth grains, as is that of 

 all the arm and disk plates. In the interbrachial space, between the pairs 

 of radial shields, a single large scale occupies the margin of the disk. 

 Under arm-plates three-sided and very small ; the outer side is nearly 

 straight, the laterals are re-enteringly curved and meet in a point within ; 

 length to breadth (5th joint) .5 : .4. Further out they rapidly become 

 smaller, and, towards the tip of the arm, are scarcely to be seen. Side 

 arm-plates very thick and swollen, meeting above and below, from the 

 very innermost joint ; at the fifth joint, their line of juncture is as long aa 

 the under arm-plate; and, further out, they constitute almost the whole of 

 the joint. Upper arm-plates very small ; longer than broad, diamond 

 shape, with the outer angle shorter than the inner one ; length to breadth 

 (2d joint from disk) .8 : .6. Genital slits extending from the outer corner 

 of the mouth-shield to a point about two thirds the distance to the margin 

 of the disk ; they are very narrow, and are bounded by two genital plates, 

 which grow wider at their outer end, and are placed in a single line ; 

 moreover, there is a very narrow plate between the inner part of the slit 

 and the side arm-plate. Arm-spines two, very short, scarcely tapering, cut 

 square oil" at the end, nearly equal ; lengths to that of the under arm-plate 

 (5th joint) .3, .3 : 1. Near the tip of the arm the under spine is toothed, and 

 hooked at the end, and the upper spine somewhat rough. There are 

 tentacle-scales on the second and third joints, one to each pore ; beyond 

 this, neither tentacles nor scales ; these scales are small, curved, and 

 broader than long, and are situated close to the inner angle of the little 

 under arm-plate, which gives them the look of being crowded towards the 

 centre of the arm. The tentacles are short and small. 



Color in alcohol, white. 



Variations. ■ — A young one had the disk 1.8 mm., the arm C mm. The 

 scales of the upper disk were swollen and distinct, though closely soldered 



