172 



OPHIOTHRIX DEMESSA. 



much the stoutest and longest, and of about equal length, viz. 2.7'"'° ; 

 sometimes, however, the upjier one is very short and stout ; three 

 lowest spines minute and slender, the longest not longer than .8'°'°- ; a 

 little farther out on arm only five spines, two large, one medium, and 

 two small. The large spines have on their flat sides diagonal rows of 

 smooth, microscopic tubercles, which give them a wavy or corrugated 

 appearance. One tentacle-scale, represented by a microscopic thorn. 

 Color, in alcohol : above, disk uniform light Indian-red ; arms dull 

 purplish, with a very distmct longitudinal line of black, bounded on 

 each side by a clear white line ; spines glassy, with a pink hue ; below, 

 mouth apparatus and under arm-plates white ; interbrachial sjDaces In- 

 dian red without, but yellowish toward the mouth. 



Variations. — The number of spines sometimes rises to nine, of which 

 five are large, and four very small. The mouth-shields, instead of being 

 regularly oval, may have their lateral corners quite sharp. 



This species may be readily distinguished from all others of Florida, 

 by the granulation of the disk, the character of the spines, and the 

 regular form of the upper arm-plates. 



LIST OF SPECIMENS. 



Catalogue Original Number 

 Number Number, of Spec. 



Locality. 



When 

 Collected. 



Whence obtained. 



Nature of 

 Specimen. 



136 



Museum of Comparative Zoology. 

 1 I Florida. I ' Prof. Agassiz. 



Alcoholic. 



Ophiothrix demessa Ltman. 



Ophiothrix demessa Lyman. Proceed. Boston Soc. Nat. Hist., \' 111. p. 82. 1861. 



Special 3farks. — Upper surface of disk, wdth radial shields closely 

 covered with minute spines, bearing a crown of thorns. Arms about 

 nine times as long as the diameter of the disk. Little thorny spines on 

 the ujDper arm-plates. 



Description of a Specimen. — Diameter of disk, lO.S"""' ; width of 

 arm without spines, 1.9°"°' ; length of arm, 97'°"'. Tooth-papilla3 fifteen, 

 unusually stout, standing on a level with each other, arranged in hori- 

 zontal rows of from two to four, according to size ; upper ones stoutest. 

 Teeth four, thick, stout, standing well apart. Mouth-shields much 



