AMPIIIURA GRACILLIMA. 



117 



outer side re-enteringly curved ; length, .3"""-. Side arm-plates with a 

 decided ridge for su]i])ort of arm-spines, encroaching above, even at base 

 of arm ; and l)elow also, farther out on arm. Upper arm-plates much 

 broader than long, pointed oval, more curved within than without, hav- 

 ing a slight median ridge; length to breadth (twelfth plate), .3 : .7 ; 

 about two thirds out on arm, plates broader than long, Ijounded without 

 b}" a nearly straight line, within by a strong arch ; overlapping each 

 other slightly, and set closer together than those nearer the base of the 

 arm. Disk-scales minute ; above, varying somewhat m size, being larger 

 near radial shields ; from 144 to 225 to a square mm. ; below, rather 

 smaller. Eadial shields sunken, very long and narrow, joined for their 

 whole length, their inner ends buried in the disk-scales ; length to 

 breadth, 1.4 : .2. Arm-spines four, close to the disk five, short, slender, 

 rounded, tapering, sharp, nearly equal ; third spine a trifle the longest ; 

 length to that of under arm-plate, .4 : .3. Tentacle-scales two, wide, 

 short, thin ; the inside one running along lateral side of under arm- 

 plate, the outside one standing at right angles to it. Color, in alcohol : 

 pale brownish. 



Variations. — The mouth-shields vary somewhat, but always have an 

 angular, ovoid outline. The Hving animal has the disk dark gray above, 

 with black radial shields, and a central fliwn-colored spot ; first three 

 arm-joints edged with black ; the rest either black or dark or light gray ; 

 along the median line of the arai, above, an interrupted white line. 

 Found at low water, six inches deep in soft mud ; it throws up one arm 

 to the surface (Stimpson). 



This species is easily told by its immensely long, slender, and even 

 anus, with slim, stout, tapering spines on their sides. 



LIST OF SPECIMENS. 



Catalogue I Ori<rinal Number 

 Nuuiber. [Number, of Spec. 



Locality. 



When 

 Collected. 



Whence obtained. 



Nature of 

 Specimen. 



Museum of Comparative Zoology. 



245 . . I 1 I Fort Johnson, Charles- | I l 



I I I ton, S. C. \ Wm. Stimpson. I Alcoliolic. 



Smithsonian Institution. 

 1029 I . . I 1 I South Carolina. ! I Wm. Stimpson. I Alcoholic. 



