132 BULLETIN OF THE 



OPHIOCHITON* gen. nov. 



Disk covered with fine, imbricated scales and small radial shields. Numerous 

 sharp mouth-papillse, with teeth but no tooth-papilliTe. Upper and under arm- 

 plates about as broad as long, and separating the side arm-plates, which project 

 slightly and are rather small. Under plates furnished with a median longi- 

 tudinal ridge. Arm-spines slender and smooth, arranged on the sides of the 

 side arm-plates, near the outer edge. Two long genital openings in each 

 interbrachial sjiace. 



The genus is allied to the true OpKiarachna, which, however, has a granulated 

 disk. 



Ophiochiton fastigatus sp. nov. 



Plate VII. Figs. 182, 183. 



Special Marks. — Four slender, smooth, taiiering, blunt arm-spines. Scaling 

 of disk very fine, with a few larger rounded plates. Radial shields small and 

 separated. About thirteen mouth-papillse to each angle. 



Description of an Individual (Station 232). — Diameter of disk 20 mm. 

 "Width of arm, without spines, close to the disk 2.8 mm. Five or six sharp 

 pointed papilla? on each side of an angle, and one shorter and more rounded 

 at the apex. Mouth-shields much broader than long, with lateral cornel's 

 rounded, a peak within and a lobe without ; length to breadth 2.3 : 3. Side 

 mouth-shields very narrow, broader without than within, where they meet. 

 First under arm-plate very small, triangular ; the other plates are four-sided, 

 with outer and inner edges nearly straight, and deep re-entering curves on the 

 lateral sides : they are highly arched, forming along the arm a longitudinal 

 ridge. Side arm-plates small, with a rather low spine-ridge, not meeting 

 below or above. Upper arm-plates broader than long, slightly arched, four- 

 sided, broader without than within ; inner and lateral sides straight, outer edge 

 slightly curved. Disk flat, with interbrachial spaces somewhat contracted, 

 covered above and below by very minute, thin, overlapping scales ; three to 

 five in the length of a mm. and somewhat larger near margin. In each brachial 

 space there is a row of small rounded scattered plates, radiating from the 

 central primary plate ; genital scales covered. Radial shields widely separated, 

 long triangular, and small, with an angle within ; length to breadth 2 : 1. 

 Four smooth, tapering, blunt, nearly cylindrical arm-spines, placed high on the 

 sides of side arm-plates near the outer edge; lengths to that of an arm-joint 

 1.8, 1.8, 1.8, 2 : 1.3. Two tentacle-scales on each pore, one large one on 

 the interbrachial and a smaller one on the brachial side. Color in alcohol, 

 pale brown ; upper disk inclining to olive. 



A smaller specimen with a disk of 13 mm. had arm TO mm. long. It was 

 similar to the adult, excejit that there usually were but three arm-spines, and 



* 6(f>is, snake ; x'^'^c, coat of mail. 



