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AMPHIURA URTICA. 



curved edge, and standing nearly at right angles to each other, the 

 inside one running along the lateral side of the under arm-plate. Color, 

 in alcohol : nearly uniform faded gray. 



Variations. — Another specimen of about the same size had the 

 scaling of the disk somewhat finer, and the radial shields almost as 

 wide as long. Mr. Stimpson says that the disk of the living animal is 

 lobulate, and very soft. The creature is of a very dark-gray color, 

 nearly black, except the white madreporic shield ; the arms jet black 

 above, except at their extremities. It hves at low water, buried in 

 the mud. 



This species is pretty distinct from other Amphiurce, and has some 

 resemblance to SemijihoUs. It seems to stand nearest to A. Riisei, 

 from which, however, it differs in having longer arms, separated under 

 arm-plates, sharper arm-spines, &c. 



LIST OF SPECIMENS. 



AmpMura urtica Lyman. 



Ampldura urtica Lyman. Proceed. Boston Soc. Nat. Hist., VII. p. 195. 



Sjjecial Marks. — Some of the disk-scales bearing fine prickles on 

 their edges. Arm-spines sharp, rounded, tapering. 



Description of a Specimen. — Diameter of disk, 6""°- ; outer side of 

 mouth-shield to outer corner of opposite mouth-slit, 2'°"' ; width of arm 

 without spines, .S""- ; length of arms about eleven times diameter of 

 disk (a specimen having a diameter of disk 5.5""°', had SS""- length of 

 arm) ; distance from outer edge of mouth-shield to inner points of 

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

 Mouth-papillae rounded and bead-like, three on each side. Teeth six, 

 rather irregular, three upper ones largest, stout, longer than broad, 

 thickened ; two next smaller and more pointed ; lowest one very short 

 and swollen, like a tooth-papilla. Mouth-shields nearly square, with an 



