MUSEUM OF COMPARATIVE ZOOLOGY. 115 
arm-plates beyond the third. Four small, equally spaced arm-spines. Small 
upper arm-plates. The great lower interbrachial plate has usually two much 
smaller at its outer corners. 
Description of an Individual (Station 24).— Diameter of disk 8.5 mm. 
Width of arm, without spines, close to disk 2 mm. Mouth-papille five on 
each side, with a large diamond-shaped one at angle of jaw, all forming a close 
line, Mouth-shields large, irregularly pentagonal, with an acute angle inward 
and outer edge straight ; length to breadth 2: 1.7. Side mouth-shields longer 
than broad, wider without than within ; outer ends curved, touching by their 
narrow ends within. Genital scales large, semicircular, stretching from mouth- 
shield to margin of disk, There are only three under arm-plates, the first 
small and diamond-shaped, lying at outer end of motth-slit ; second and third 
pentagonal, with an angle inward, and lateral and outer sides nearly straight. 
Side arm-plates thick, slightly swollen, and beyond the third under arm-plate 
forming the entire covering of the arm, with the exception of rudimentary 
triangular upper arm-plates, which do not extend to the tip of the arm. Disk 
rather flat, and covered by closely soldered plates ; the upper surface is occupied 
by six primary plates, separated by many smaller ones ; radial shields rounded 
triangular, with acute angle within ; outer edges curved, strongly diverging 
inward, and separated by a triangular scale, In interbrachial space are two 
angular plates, the outer one wide quadrangular and closely soldered to a 
great marginal plate, which, with the genital scales, covers the interbrachial 
space on the under surface of the disk. At base of arm above are four little 
plates, two central and two lateral. Four short, blunt, and thick arm-spines, 
situated low on the outer edge of the side arm-plate. Tentacle-scales minute, 
rounded, situated on the inner angle of second and third under arm-plates. 
Color in alcohol, pale gray. 
In presence of the many new species of Ophiomusiwm, it has been thought 
well to give figures and a full description of this one. 
Station 24, off St. Thomas, 390 fathoms, 2 specimens, Station 23, close to 
Sombrero, 450 fathoms, 3 specimens, 
Ophiomusium simplex sp. nov. 
Plate I. Figs. 10, 11. 
Special Marks. — Most of the lower interbrachial space outside the mouth- 
shield is occupied by broad genital scales and a great central plate. No under 
arm-plates beyond the third. Two minute arm-spines set low down. Besides 
the great interbrachial plate below there are three others along the margin. 
Description of an Individual (Amboyna). — Diameter of disk 6 mm. Width 
of arm without spines 1.5 mm. ; length of arm 15 mm. Mouth-papille seven 
on each side, and one, spearhead-shaped, at angle of jaw, closely soldered 
together and forming a slightly raised continuous line. Mouth-shields little 
longer than broad, pentagonal, with acute angle within, at the corners of 
