OPHIOCOMA ^ETIIIOPS. 79 



like flattciKHl, rounded wedges, somewhat narrower witliin than without. 

 Mouth-shields ohlong, with rounded corners ; length to breadth, 4 : 3. 

 Side mouth-shields small, rather variable in size, triangular ; length to 

 breadth, 1.5:1. Under arm-plales s(|uarish ; lliiid. fourth, (il'th, and 

 sixth plates of nearly e(|ual size, and sniaUer than those beyond, their 

 lateral sides nearly straight, their outer and inner sides a little curved, 

 length to breadth, 2:2; seventeenth plate typical in shape, outer side 

 sliglitly curved, lateral sides straight, and sloping a little inward and 

 towards each other, inner side making rather a strong curve ; length to 

 breadth, 2.o : 2.3 ; about two thirds out on arm, plates almost s([uare, 

 with straight sides, and corners a little rounded, length to breadth, 

 1.7 : 1.7 ; close to tip of arm, plates twice as long as broad, elongated 

 oval, broader without than witliin. Side arm-plates encroaching on 

 upper and lower arm-})lates, sometimes nearly meeting below, and thus 

 slightly separating two neighboring plates ; they do not properly meet 

 above and below till close to tip of arm. Upper arm-plates much 

 broader than long, shaped like a narrow oval, with pointed corners ; 

 near base of arm, length to breadth, in l^roader ones, 2.2 : G.5 ; in nar- 

 rower ones, 2.2 : 5. First plate rudimentar}', very short and narrow, 

 partly covered by granulation of disk ; second, third, and fourth plates 

 rather narrower than those just beyond, and often stouter, so that the 

 arm looks constricted at its base. The plates maintain the same gen- 

 eral shape and proportions till close to tip of arm. Granulation of disk 

 close, fine, and bead-like, both above and below; near base of arms 

 above, coarser and more scattered ; about 30 grains to a square mm. 

 where granulation is thickest ; below, granulation reaches nearly, or 

 rpiite, to edges of genital slits. Arm-spines stout, rounded, somewhat 

 flattened, the lowest ones most so, increasing in thickness from below 

 above ; near base of arm, usually four. Second, third, and fourth joints 

 each Avith three small, very flat spines, lowest one usually longest, some- 

 times 2°""- ; on next three or four joints, spines grow more rounded and 

 tapering, in number three, four, or rarely live ; on seventeenth joint, 

 typical spines, lengths to that of under ;u'm-plate, 5, 4.5, 4, 4 : 2.3 ; 

 beyond this, joints with three and with four spines usually alternate 

 till a point about three fourths the length of the arm, after which there 

 are only three slender, rounded, tapering spines, of nearly equal length 

 and thickness. Tentacle-scales nearly regular oval, a little pointed 

 without, rather thick, length to that of under arm-plate, 1 : 2.3 ; only 

 one on each pore, except pores of second joint, and a few others scat- 

 tered, which have two. Color, in alcohol : above, dark, rich vandyke- 

 brown, disk irregularly and obscurely radiated with darker and lighter ; 

 Ik'Iow, interl)rachial spaces uniform brown ; rest same color, but con- 

 siderably ligliter. 



