130 



AMPHIURA OCCIDENTALIS. 



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



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



Sjjecial Marks. — Moutli-papillce of nearly equal size. Arm-spines 

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



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

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

 width of arm without spines, LS"""*. 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-papilla?, to that between outer corners of mouth-slits, 1.2 : 1. 

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

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



the second from the top largest ; lowest one of all 

 smallest, very short, thick, and rounded, somewhat 

 like a tooth-papilla. Mouth-shields small, oval dia- 

 mond-shaped, the angles being so rounded as to 

 give almost a true oval ; outer angle making a very 

 slight peak ; length to breadth, .4 : .5. Side mouth- 

 shields not meeting within. Under arm-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 

 Pij,. 13 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 mrn. ; 

 primary plates distinguished by greater size. Ra- 

 dial shields shaped 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. 



Amphiura occiilentalis. 

 (L'pper side.) 



Amphiura occidentalis. 

 (Lower side.) 



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

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



