OPIIIOPLOCUS IMBRICATUS. G9 



Ophioplocus imbricatus Lyman. 



OphioJepls imhricata Mill. & Tuuscu. System di-r AstericU'ii, p. 93. 

 Ojjiiioplacus tcxaellatus Lymax. True. Boston 8oc. Nat. Hist., VIII. p. 70. 1801. 



Special JIark.'<. — Color gray, with olj>^curo cross-baiuls on the arms ; 

 length of arms, m adults, four to five and a half times the diameter of 

 the disk. 



Description of a Specimen. — Diameter of disk, 17""" ; width of arm 

 without spines, 3.5"""* ; length of arm, 70""° ; mouth-papilla}, five on 

 each side, and one odd one, placed just under the teeth ; the side 

 papilla* squarish, flat, and crowded, the odd one resembling the teeth. 

 Teeth live, thick, short, stout, broader than long, with a curved cutting 

 edge. Mouth-shields broad heart-shape, with a curve without and an 

 angle within ; length to breadth, 1 : 1.5. Side mouth-shields large, and 

 of even width, .S"""' M'ide. Under arm-plates squarish, very regular and 

 clear in outline, slightly separated, thick ; outer side curved, lateral 

 sides a little re-enteringl}- curved ; length to breadth (tenth plate), 

 1 : 1.3. The halves of the upper arm-plates are rounded triangular, 

 very much like the supplementary pieces in Op)hionereis ; at the base 

 of the arm they lie very low down, so that the side arm-plates are 

 much reduced m size ; they are sei)arated from each other by six sup- 

 plementary pieces, of which one lies on the middle line of the arm, 

 and the other five make a sort of semicircle round it ; at the base of 

 the arm the central piece of this semicircle becomes very small indeed, 

 and is often divided in two ; between the supplementary pieces there 

 are sometimes single large grains. The halves of the upper arm-plates 

 and the supplementary pieces are thick and swelled, and often of about 

 the same size. Side arm-plates small, and almost covered up by the 

 arm-spines. Scales of the disk a little larger above than below, mostly 

 overlapping, but with here and there a round scale, varying somewhat 

 in size, the largest .8""°' long. Radial shields very small, about 1°"° long, 

 sunken in the scaling of the disk. Genital slits only 2°"" long, starting 

 !"""• outside the mouth-shield. Arm-spines three, stout, round, blunt ; 

 the lowest much the largest ; lengths to that of under arm-plate, .8, 1, 

 1.3 : 1. Tentacle-scales two, longer than broad, flat, nearly oval. Color, 

 in alcohol : gray, with very obsciu'e cross-bars of darker on the arms. 

 According to a colored sketch l3y Mr. Garrett, the tints of the living 

 animal are about the same. 



Variations. — The characters of fifteen specimens w^hich I have 

 examined were very uniform, only the 3'oung have shorter arms. 

 The proportions of the disk to the arms in specimens of diflerent sizes 



