﻿130 AMPHIURA OCCIDENTALIS. 



Amphiura occidentalis Lyman. (Figs. 12, 13.) 



Amphiura occidentalis Lyman. Proceed. Boston Soc. Nat. Hist., VII. p. 194. 1860. 



Special Marks. — Mouth-papillae of nearly equal size. Arm-spines 

 very blunt, and pretty stout. Arms long, flat, broad. 



DescrijJtion of a Specimen. — Diameter of disk, 5.8""- ; outer edge 

 of mouth-shield to outer corner of opposite mouth-sUt, 2.2'"°'- ; greatest 

 width of arm without spines, l.S"""'. As the arms were somewhat 

 broken, their length could not well be measured ; but, from their pro- 

 portions, they must have been at least eight times the diameter of the 

 disk. Distance from outer side of mouth-shield to inner points of 

 mouth-papilliB, to that between outer corners of mouth-slits, 1.2 : 1. 

 Mouth-papillae rounded ; innermost one stoutest, and pointing to centre 

 r,^, 12 of mouth. Teeth five ; four upper ones flat, square, 



^^^^^^ the second from the top largest ; lowest one of all 



^j^^^^^W^i smallest, very short, thick, and rounded, somewhat 

 ^^^^HH^^Pr lilve a tooth-papilla. Mouth-shields small, oval dia- 

 ^lip|BP''^ mond-shaped, the angles being so rounded as to 



^^^ give almost a true oval ; outer angle making a very 



Amphimaoccuientaiis. sllglit pcak ; leiigth to breadth, .4 : .5. Side mouth- 

 (uppers.rte.) shields not meeting within. Underarm-plates square 



oblong ; angles somewhat rounded ; outer side with a slightly re-entering 

 curve ; second plate differs from the rest, being five-sided, with its fifth 

 angle directed inward ; it is separated from the rudimentary first plate 

 by narrow prolongations of the side arm-plates. The next three or 

 four plates are in like manner separated, while those farther out on the 

 j..„ -,., arm are close together, which is an inversion of the 



usual order. Length of plates to breadth, .4 : .4. 

 Upper arm-plates oblong, with rounded corners ; 

 outer side with a slightly re-entering curve ; length 

 to breadth, .5:1. Scales of disk fine, smooth, and 

 even, above and below ; about 60 to a square mm. ; 

 primary plates distinguished by greater size. Ra- 

 cLowerside.) ^.^^-^ shields shapcd like an elongated, blunt pear- 



seed ; separated by a narrow, single line of scales ; length to breadth, 

 1.1 : .4. Arm-spines three, not tapering, rather stout, rounded at the 

 end, flattened, about as long as the joints. Two small, rounded 

 tentacle-scales. Color, in alcohol : disk, above, faint greenish-gray ; 

 arms and under surface straw-color. 



Variations. — The mouth-shields may be quite oval ; the second 

 under arm-plate, instead of being five-sided, may resemble the rest. 



