14 OPHIOMITRA CERVICORNIS. 



.4 : .4. Disk soft and smooth; naked below; but thin imbricated scales 

 may be distinguished above. There are some scattered spines, which are 

 pointed, a little rough, and not over .2°""- long. Radial shields not conspic- 

 uous, oval ; touching at their outer points, but separated within by a scale. 

 Arm-spines three, slender, rounded, tapering ; the upper one the longest, 

 Qmm. Qj^g tcntacle-scale, which is small, spiniform, and placed on the side 

 arm-plate. The tentacles are smooth and rather thick. 



Color, in alcohol, pale greenish-gray. 



Hassler Expedition; Juan Fernandez, 240 fathoms. 



The genus Ophiacantha, as now limited, contains species which vary ex- 

 tremely from the type 0. setosa. Indeed, there is no genus in which the 

 admitted species are so varied in their detail of structure. 0. marsiqnalis may 

 be placed in it as properly as some other species already there ; and that, too, 

 despite the fact that the mouth-parts and under surface in general recall, to 

 a certain extent, Ophioscolex. The interbrachial pouches had large young 

 ones in them, whose arms protruded through the genital openings. 



Ophiomitra cervicornis pp. nov. 

 PI. II. f. 10, 20. 



Special 3Iarks. — Ten mouth-papillse, whereof three are on each side of the 

 jaws ; two at the apex, under the teeth ; and two on the under surface of the 

 jaws on each side of the median line. One tentacle-scale, having the form 

 of a small toothed plate. 



Description of an Individual — Diameter of disk, 8™""-. Width of arm without 

 spines, 2.5''""-. Length of arm about 42™"-. Mouth-papillge ten, all blunt, 

 stout, spiniform, except the outer one on each side, which is rounded like a 

 very thick scale : there are three on each side of the jaws ; two at the apex, 

 under the teeth ; and two on the under surface of the jaws just inside the 

 junction of the side mouth-shields. Mouth-shields diamond-shape ; length 

 to breadth, 1 : 1.2. Side mouth-shields short, straight, of nearly equal width, 

 meeting within. Under arm-plates hexagonal, with the lateral angle cut off, 

 where the tentacle comes out ; length to breadth, .8 : 1. The first plate, at 

 the corner of the mouth-slit, has its sides bent downwards, making a sort of 

 sheath for the mouth-tentacle. Side arm-plates stout, meeting above, but 

 not below, having a prominent ridge for the arm-spines. Upper arm-plates 

 triangulai-. with an angle inward and the outer side curved ; length to 



