OPIIIOPIIOLIS BELLIS. 97 



nL\irly straight, and a little shorter than the outer ; outer side nearly 

 straight; outer corners strouglj' rounded; length to breadth (twelfth 

 plate), 1.2 : 1.7 ; the iu-st six plates are proportionately longer, and 

 much luore rouuded, than those beyond ; their outer side often has a 

 slightly re-entering emve ; at the tip of the arm the i)lates are longer 

 than broad, with the outer and lateral sides quite straight, and an angle 

 at the inner end. Side arm-plates encroaching a little below, between 

 under arm-plates ; cleanly separated from each other by naked skin. 

 Up})er arm-plates nearly oval, stout, sometimes broken in two ; length 

 to breadth (third plate), 1.2 : 1.1). Supplementary pieces ten or twelve, 

 very closely wedged together, and variously distorted, often broken in 

 tw o ; those on the sides sometimes encroaching between the rows of 

 arm-spines. Near the end of the arm, upper arm-plates nearly round ; 

 supplementary pieces bead-like, not crowded. Disk closely beset, above 

 and below, with short, flattened spines, except on the primary plates, 

 and a small space outside the mouth-shields ; these spines vary in 

 length, being short and granular towards the middle of the disk and 

 at the bases of the arms, but longer and more closely set in the inter- 

 brachial spaces below ; their greatest length is about .7"""" ; primary 

 plates rounded, the middle ones smallest ; some of those in the inter- 

 brachial spaces often overgrown by spines ; the largest ones having a 

 diameter of 1.7°""'. Radial shields having the form and appearance of 

 primary plates. Arm-spines six, stout, tlattened, cut square off at the 

 end ; four upper ones nearly equal, very broad, fiat, and square ; two 

 lower ones smaller and more conical ; lengths to that of lower arm-plate 

 (ninth joint), 1.5, 1.5, 1.5, 1.3, 1.3, 1.1 : 1.2 ; towards the end of the arm, 

 spines rounded and conical, usually five ; lowest spine on tip joints 

 armed with hooks. Tentacle-scale nearlv round, stout, flat ; lenu'th to 

 that of under arm-plate, .6 : 1.2 ; towards the end of the arm the 

 tentacle-scales are much longer than broad, and are nearly as long as 

 the under arm-plates. Color, in alcohol : above, dull brownish-red (lake 

 and burnt-undjcr) somewhat variegated ; below, interbrachial spaces 

 same as upper surface, but much paler ; the rest yellowish. 



Variations. — Even in alcohol the coloration is seen to be quite 

 changeable ; sometimes the upper surface is uniform dull brownish-red, 

 of different shades in different specimens ; or the disk may be nearly 

 white, with reddish arms ; or both arms and disk may be mottled red- 

 dish and yellowish. Professor Agassiz's colored drawings show that of 

 the living animals scarcely two are alike. The principal patterns are : 

 disk and arms brownish orange, more or less variegated ; disk dark 

 green, with a light-green central star, light-green banded arms, and 

 white radial shields ; disk and arms indigo blue, variegated with green- 

 ish and reddish ; disk with a light centre and dark margin, and light- 



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