MUSEUM OF COMPARATIVE ZOOLOGY. 105 



Station 164, 950 fathoms, 1 specimen. Station 1C5, 2600 fathoms, 1 speci- 

 men. Station 1G6, 275 fathoms, 1 specimen. Station 218, 1070 fathoms, 2 

 specimens. 



OPHIOPLINTHUS * gen. nov. 



Disk smooth and covered by a thin skin bearing irregular delicate scales and 

 radial shiehls. Genital scales Avide and divided in several pieces. Small, 

 bhmt, close-set niouth-papillas ; no tooth-papilla) ; short angular teeth ; very 

 minute, peg-like arm-spines on outer edges of side arm-plates. Second pair of 

 mouth-tentacles and first two pairs of arm-tentacles rising from round pores near 

 the inner end of the under arm-plates ; those beyond are smaller, and stand 

 close to the under arm-spine. Arms narrow, cylindrical, and gradually taper- 

 ing. Two genital openings, running only a part of the way toward the margin. 

 Mouth-frames seen from above, after removing the top of the disk, long and 

 rising in a ridge, so that in the interbrachial space is a wide angle, and in the 

 brachial space a deep trough. Arm-bones long and cylindrical, with only a 

 faint upper furrow. Genital scales long, slender, and cylindrical. 



This genus by its large first under arm-plate has a slight relation to Opliio- 

 glypha, and by its large tentacle-pores at base of arm, an appearance like Ophio- 

 musium, but its structure is really q^uite peculiar. 



Ophioplinthus medusa sp. nov. 



Plate II. Figs. 30. 31, 40. 



Special Marks. — Scaling of lower interbrachial space coarse (four or five scales 

 in a transverse row). No scales on arm-tentacles. Usually three very minute, 

 peg-like arm-spines, equally spaced. 



Description of an Individual (Station 156). — Diameter of disk 16 mm. 

 Width of arm 2 mm. Mouth-papilla; short, square, closely soldered, four or 

 five on each side, with one, diamond-shaped, at ape.x of the jaw. Mouth-shields 

 rounded triangular, with an angle inward, sides curved, and often a re-enter- 

 ing curve without ; they are frequently furrowed or cracked. Side mouth- 

 shields irregularly rhomboidal, sometimes broader within, where they touch. 

 First under arm-plate rounded triangular, with a blunt angle inward, and a long 

 curved outer edge ; second plate five-sided, with an obtuse angle within, and a 

 curved outer edge ; beyond this they are broader than long, with a blunt angle 

 within and a wavy curve without. Side arm-plates thick and smooth, meeting 

 broadly below and touching above beyond the si.\th plate. Upper arm-jilates 

 rounded diamond-shaped, with a longer angle within ; thej' often are cracked 

 or grooved. Disk high, covered with thin, irregular, overlapping plates ; the 

 central primary one about 2 mm. in diameter and conspicuously the largest, 

 and in each brachial space is a primary plate larger than the rest. Radial 

 shields irregular, foui'-sided, with rounded corners, broader on the outer edge, 



* 6<f>ii, snake ; Tr\lvdos, tile. 



