259. 



Width of arm, without spines, 1.2 millim. Length of arms, 40 

 millim. Mouth-papilli\j 10 or 11 to each angle of the mouth, 

 small, rounded, somewhat flattened. Teeth 4, thin, flat, squarish ; 

 lowest one thicker, and with a rounded cutting edge. Mouth- 

 shields much rounded, heart-shaped, with narrow end inward ; 

 length to breadth, 1 : .9. Side mouth-shields short, triangular, 

 widely separated within. Under arm-plates squarish, a little 

 longer than broad ; outer side slightly curved, lateral sides a lit- 

 tle reenteringly curved ; length to breadth, (17th plate,) .5 : .4. 

 Upper arm-plates triangular, with a rounded angle directed out- 

 ward, and a sharp angle directed toward each side ; length to 

 breadth, (11th plate,) .5 : .9. Supplementary pieces as long as 

 the joints, triangular, with the- outer side curved. Disc-scales 

 very close and fine ; about 200 to a square millim. Radial 

 shields very small and narrow ; about .7 millim. long. The usual 

 comb of papillce along the genital slits is not much developed. 

 Arm-spines 3, rather short, and flattened ; cut off square at the 

 end ; middle one longest ; lengths to that of under arm-plate, 

 (17th joint,) .7, 1.2, .9 : .5. Tentacle-scale 1, large, round, thin. 

 Color, in alcohol : disc faint greenish gray, finely lined with 

 brownish ; above the base of each arm a dark purple fork, of two 

 converging lines ; sometimes a few other veins of dark purple ; 

 arms brownish straw-color, with a faint, broken line of whitish 

 running lengthwise; at intervals of from 5 to 12 joints, a dark 

 purple joint, making a cross-band ; below, interbrachial spaces 

 same as upper surface ; other parts light straw-color. 



Variations. The dark markings at the base of the arms may 

 differ somewhat in shape and size ; and the arm-bands may go 

 entirely round, or be confined to the upper surface. A small 

 specimen, with a disc of 4.2 millim., had arms of 22 millim. The 

 number of disc-scales to a square millim. was about the same 

 as in the larger ones. The lower arm-plates were longer and 

 more concave on their lateral sides ; the teeth had all rounded 

 cutting edges ; the spines were more rounded and tapering than in 

 the adult ; the radial shields could hardly be distinguished. The 

 mouth-shields vary a little, in being more or less rounded. 



0. Xantusii differs from 0. annulata in having shorter and 

 blunter arm-spines, and shorter arms ; the color also is different ; 

 from 0. reticulata in blunter arm-spines, shorter arms, and a dif- 

 ferent pattern of color. 



