OPIIIOCOMA ECIIIXATA. 83 



running along their edge ; their inner ends are separated by a bridge 

 of about one half the width of the mouth-shields. Arm-spines of mod- 

 erate length, and two ui)per ones quite stout. Second joint three 

 spines, small and flattened, with rounded ends ; lengths to that of lower 

 arm-plate : upper, .8 : 1.8 ; lowest, 1.8 : 1.8 ; middle, 1.2 : 1.8 ; third and 

 fourth joints have three spines ; the fifth, and those immediately 

 beyond, four. Five spines on each side are rare ; at about one fourth 

 the length of the arm there again begin to appear only three spines, 

 and ioints bearinii: this nund^er often alternate with lliose haviuii; four: 

 still farther out, as many as four spines become rare, and near the tip 

 of the arm there are only three. Fifteenth joint four spines, lengths to 

 that of under arm-plate, 3.6, 3.2, 2.4, 2.4 : 1.6 ; the upper spine is much 

 the largest ; it is rounded, slightly curved, flattened, and tapering, and 

 is very stout ; its greatest thickness to its length as 1.2 : 3.6 ; the next 

 lower is of about the same proportions, but somewhat less stout ; the 

 two lowest are more tapering, and much more flattened. These four 

 may be considered the characteristic spines of the species ; the upper 

 spine is the most variable, and may have a proportionate length as 

 great as 4.2 ; as they approach the end of the arm, the spines become 

 proportionately longer, more slender, and less flattened ; lengths to 

 that of under arm-plate, 3, 1.6, 1.8 : 1.2 ; the two lower ones are still 

 much flattened, but the upper one is nearly cylindrical, and varies in 

 length from 2.4 to 3.6 ; at the tip of the arm the upper spine has quite 

 lost its stout, blunt character, and has become very slender ; the lengths 

 of spines to that of under arm-plate, 1.4, 1.2, 1.2 : .8. There are two 

 tentacle-scales to each pore, and this number continues for about three 

 fourths the length of the arm, when pores with only one scale begin to 

 appear ; sometimes there will be several such, followed by several more, 

 each with two scales, but the last joints have but one scale to each 

 pore ; near the disk their length is to their breadth as 1 : .4, they are 

 much flattened, widest near the top, somewhat contracted at the base ; 

 the inner is usually a trifle the longer ; they stand close, side by side. 

 Color, in alcohol : roof of the disk light brown, mixed with some light- 

 Inownisli gray, and ten indistinct radiating lines of the latter color ; 

 below, interbrachial spaces similarly colored, but the edges of the geni- 

 tal slits are nearly white ; the ground color of the mouth-papilla?, side 

 mouth-shields, and mouth-shields, is nearly white, but they are more or 

 less clouded with light brown ; the under arm-plates, for one fourth or 

 one third the length of the arm, are whitish, with a large spot of 

 brown ; farther out the plates are entirely brown. The side arm-plates 

 are yellowish, finely mottled with light brown. The upper arm-plates 

 are purplish brown, with one, two, or three plates at varying distances, 

 nuich lighter colored, thus giving an irregular barred appearance. The 

 upper and second arm-spines are light purplish-brown, their points and 



