168 OPHIOTHRIX SPICULATA. 



length as great as 3. 5""°", and sometimes even 3.8""°- ; eighth joint, seven 

 spines ; lengths to that of under arm-jDlate, 3, 3.2, 2.3, 1.5, 1.6, .4 : .6. 

 Tentacle-scale, instead of being spiniform, is flat and square, ending in 

 four or five microscopic points. Color, in alcohol : above, faded cobalt- 

 blue, with a brownish tinge towards centre of disk ; along centre of 

 arm a faint line of lighter ; below, interbrachial spaces pale cobalt-blue ; 

 other parts the same, but lighter. In the living animal " the body is 

 dark fuscous above, and pnle beneath ; every fifth ventral plate on the 

 arms is sometimes red or jjrown," and the apex of the arm-spines is fre- 

 quently black (LeConte) ; or the main color may be greenish, the upper 

 arm-plates violet, and every fourth joint red (Dr. Orsted). 



Variations. — Either this species is very variable, or else there are 

 two or more species at present confounded under it. The specimen 

 above described may be considered as the type ; from which, however, 

 there are considerable deviations, both in the armature of the disk and 

 the length of the arm-spines, A specimen with a disk of 8°""" had the 

 disk closely covered with short spines, bearing each a crown of from 

 three to six thorns ; there were no long spines on the disk ; the seventh 

 arm-joint bore eight spines, whose proportions to that of the lower arm- 

 plate were as follows : 1.8, 2.2, 1.8, 1.2, .7, .6, ,5, .4 : .6. The second spine 

 was remarkably flat, and was cut square off at the end ; it had thirteen 

 thorns on each side. Another specimen, with a diameter of disk of 

 11.5""", had from seven to nine spines on the basal joints; the length 

 of the three upper ones to that of the lower arm-plates being about 

 4.7, 4.5, 4.1 :,7. This specimen had the radial shields nearly naked, but 

 the rest of the disk pretty closely covered with short and long spines. 

 A comparison of the length of the longest arm-spines with that of the 

 lower arm-plates gave, in eight well-grown specimens, an average of 

 3,1 : .6, the extremes being 5 : .7 and 2.4 : .6. In other words, the disk 

 may have many or few spines, and may have either one or two sorts ; 

 and the arms may have spines of from four to seven times the length 

 of a lower arm-plate, and differing more or less in shape. A young 

 specimen had the disk 2°""-, arms 10'"""', arm-spines .7°""', under arm- 

 j^lates .2'""- ; the arm-spines had five thorns on each edge ; the disk w^as 

 thinly covered w ith short spines ; the under arm-plates were longer 

 than broad, widest without, and had a notch in their outer side. 



O. spicidata resembles 0. violacea and 0. angulata, but differs from 

 both in the greater proportionate length of the arm-spines ; from 0. 

 Orsfedli it is distinguished by different armature of the disk, different 

 pattern of coloration, and longer arm-spines. It is further remarkable 

 as a variable species. 



