MUSEUM OF COMPARATIVE ZOOLOGY. 325 



diamond-shape. Disk completely covered, above and below, with very 

 minute stumps, each of which bears a crown of microscopic thorns; on the 

 back of the disc there are about 250 to a square mm. Radial shields 

 entirely obscured, except just over the arms, where their outer ends are 

 indicated by two little swellings. Arm-spities rounded, tapering, transpar- 

 ent, and very slender ; under the microscope they appear finely prickly ; 

 on the basal joints six, of which the upper three are much the longest ; 

 lengths to that of the under arm-plate (4th joint) 1.5, 1.8, 1.8, 1.2, 1., .8 : .4. 

 The two joints within the disk have but three spines, which arc short, equal, 

 flattened at their base, and quite rough. The end joints have three spines, 

 also quite rough, and proportionately shorter and stouter than those of the 

 basal joints, but there are no hooks, or toothed spines. Tentacle scales flat 

 and sharp pointed, one to each pore. Color, in alcohol, pale blue gray for 

 the disk, and white for the arms. The description given by Liitken of 0. 

 peraacrimis corresponds pretty nearly to this species. Tliere is, however, one 

 arm-spine less in 0. meridionalis, and the underarm-plates appear to be of a 

 different shape. Only a comparison of originals can determine the doubt. 

 In 23 7 and 327 fathoms. 



Ophiomitra Lyman, gen. now* 



Testh : numerous, snull, nearly equal mouth-papillae ; no tooth-papilhe. 

 Disk flat, circular, and erect, covered with scales and radial shields, and 

 beset with thorny spines, or stumps. Arm-spines rough. Side arm-plates 

 large ami nearly or quite meeting above and below. 



So far as concerns the arms and the chewing apparatus, this is an 

 Opliiacanlha : but the disk, with its naked scales and conspicuous radial 

 shields, s-epaia f es it from that genus, which is characterized by the long, 

 very narrow, radial shields, covered, together with the disk, by a thick skin 

 bearing more or less thorny appendages. 



Ophiomitra valida Lyman, sp. now 



Special Marks. — Disk beset with thorny stumps ; arm-spines about 9 ; 

 the upper ones a little tapering, the lower ones flattened. 



Description of a Specimen. — Diameter of disk 12 mm. Length of arm 

 about GO mm. Mouth-papilla; stout, rounded, tapering to a blunt point; 

 from 10 to 11 to each angle of the mouth ; of which one or two point 

 directly inward. Teeth long, Hat, tapering to a blunt point ; 8 in number. 

 Mouth-shields small, of a rounded diamond form, with a peak within ; 

 length to breadth 1.5 : l.S. The madreporic shield has an ill-defined cir- 

 cular depression. Side mouth-shields large, meeting within, of a rude 

 oval shape. They are quite as huge as the mouth-shields proper. Under 



* 5<£ts, a snake; juiYpa, a cnp. 



