MUSEUM OF COMPARATIVE ZOOLOGY, 153 
most mouth-papila.* Mouth-shields small, as long as broad, shield-shaped, 
with a well-marked obtuse angle inward and outer margin sometimes turned 
down; length to breadth 2: 2.3. Side mouth-shields broad and thick, a 
little widest at outer ends. Under arm-plates large, thick, and regular, much 
wider than long, reaching at their outer edge entirely across the arm ; cleanly 
curved without, re-enteringly curved on sides, and having a little peak within 
where separated from next plate. — First plate small, narrow wedge-shaped, 
Upper arm-plates somewhat swollen, widely separated, wider than long, 
bounded without by a gentle curve, and within by an obtuse angle or a deep 
curve, Side arm-plates prominent and meeting freely above and below. Disk 
thick and rising well above the arms, with a very deep, narrow constriction 
and furrow in each interbrachial space. The space between this furrow and the 
radial shields is on either side occupied by four large plates running diagonally 
inward, whereof one or more are often broken in two. The central disk is 
sunken, and covered by small, coarse, irregular scales, which, with the larger 
plates, are sparsely beset with short, blunt, usually smooth stumps or spines, 
which form also an irregular clump over each arm. Radial shields deeply sunken 
in a furrow, widely separated by a high ridge of irregular scales, much longer 
than broad, presenting an acute angle inward ; length to breadth 3 :.8. Near 
base of arm six stout, very thorny, glassy, blunt, cylindrieal arm-spines, the 
lowest ones much the stoutest; lengths to that of an arm-joint 3.6, 3.6, 2.8, 
1.7, 1.7, 1.7 : 1.2. Two thirds out on the arm the spines are more slender, 
and the second much longer, attaining to 5 mm. The under spine is marked 
by its thickness ; beyond base of arm it is somewhat curved. Tentacle-scales 
large, thick, pointed, flattened, sensibly smooth, except towards end of arm, 
where they bear two or three microscopic thorns, Color in alcohol, dull straw. 
It is not easy to say how much of the peculiar creasing of the disk and sinking 
of the radial shields is due to the contraction of the animal drawn from a depth 
and immersed in strong alcohol, and how much is natural. Of nine specimens 
one had radial shields much wider and more nearly on a level with the disk ; 
but in the rest the radial shields were deeply sunken, Six specimens from 
the “Blake” expedition (Agassiz and Sigsbee, 1878) seemed a variety of this 
species. They were from 480 to 860 fathoms, near Cuba. All had the radial 
shields not at all sunken and of a broad pear-seed shape ; only the centre of 
the disk bore stumps, which were little articulated cylinders bearing a crown 
of thorns. The largest specimen, with a disk of 8 mm., had seyen arm-spines, 
which were stouter than in “ Challenger” specimens and shorter, their lengths 
being 2, 3, 2.2, 2, 1.5, 1.5, 1.2; and the lowest spine, though thick, was 
scarcely or not at all curved, The other specimens were young, and had long 
slender arm-spines, and the under one curved. The “Challenger” specimen. 
from Station 33 resembled these. 
Station 3, 1530 fathoms, 3 specimens. Station 33 (var. ?) 300 fathoms, 3 
specimens. Station 84, 1124 fathoms, 3 specimens. 
* The nomenclature of the various papilli of the mouth is of course conventional, 
In most cases the lowest tooth may also be called the innermost mouth-papilla, 
