104 BULLETIN OF THE 



OPHIOMASTUS * gen. nov. 



Disk arched and extremely bigh, covered with a few large thick plates, 

 among which the primaries are conspicuous for superior size. Arms short, with 

 large thick side arm-plates. First under arm-plate similar to and nearly as 

 large as those beyond. Mouth-papilla) arranged in a narrow close-set line ; 

 teeth rather slender ; no tooth-papilla?. Small smooth arm-spines arranged 

 along outer edge of side arm-plates. Two narrow genital openings in each in- 

 terbrachial space. 



Ophiomastus tegulitius sp. nov. 



Plate VI. Figs. 167-169. 



Special Marls. — Two very short, stout arm-spines. Disk-plates swollen 

 and microscopically tuberculous. Side mouth-shield of a pointed ovoid shape. 



Description of an Individual (Station 165). — Diameter of disk 4 mm. 

 Length of arm about 6 mm. Width of arm close to disk, without spines, 

 1 mm. Mouth-papillGB so closely soldered as to form an almost continuous 

 narrow line from side mouth-shields to apex ; on either side is a long curved 

 one, followed by two shorter, and by a narrow spine-like one at apex of angle. 

 Mouth-shield pentagonal, with an angle inward, longer than wide ; inner lat- 

 eral sides straight, outer lateral corners rounded ; length to breadth .7 : .5. 

 Side mouth-shields large, swollen ; broadest and rounded within, where they 

 meet, then tapering outward along the inner lateral sides of the mouth-shields. 

 Under arm-plates long pentagonal, with an angle inward, lateral sides re- 

 enteringly curved, outer side slightly curved. Side arm-plates large, thick, 

 and swollen, meeting below and above ; upper arm-plates small, first one dia- 

 mond-shaped, and second triangular with sharp angle inward and outer edge 

 straight ; the rest are similar, but grow rapidly smaller. Disk highly arched and 

 rounded ; in the centre a large hexagonal primary plate, surrounded by six oth- 

 ers, much swollen, with inner and lateral sides nearly straight and outer edges 

 rounded ; these seven plates cover almost the entire upper surface of the disk ; 

 in the upper interbrachial space there is a rounded, much swollen marginal 

 plate, and over the arm two small, joined, scale-like radial shields. On the 

 under surface, outside the mouth-shield, there are two large plates, the outer 

 and larger one connecting with the large marginal plate. Genital scale long and 

 widf . and composed of three pieces. Tentacle-scales long, narrow, and curved, 

 the one on the interbrachial side being semicircular, while the other on the lat- 

 eral side of the under arm-plate is small and lip-like. Two very short, blunt 

 arm-spines, placed low on the outer edge of the side arm-plate. Color in alco- 

 hol, pale straw. 



A smaller specimen, with a disk of 2 mm., showed no special variations, ex- 

 cept that the radial shields were relatively larger and there were only six pri- 

 mary plates, which is doubtless the normal number. 



* 6<t>it, a snake : /xaards, a breast. 



