172 Papers from the Marine Biological Laboratory at Tortugas. 
with strong longitudinal muscle bundles of relatively coarse strands. Stro- 
bile, so far as certainly seen, filiform. First distinct segments about as long 
as broad, nearly circular, so that the first five, in one specimen, made a 
moniliform portion of the strobile; succeeding segments rod-shape, very 
much longer than broad, and rather loosely attached, margins finely crenate. 
Details of the anatomy were not certainly made out for ripe segments, but 
are probably much like those of P. brevispine. The two species may be 
distinguished from each other by means of the hooks, which present quite 
marked differences besides that of size. 
From the nurse-shark (Gingliostoma cirratum), July 2, two; July 5, six. 
All small, with no mature segments. 
Dimensions of living specimen in millimeters: Head, length 0.35, breadth 
0.35; bothria, length 0.35, breadth 0.21; length of hooks, base not included, 
larger 0.06, smaller 0.03; diameter of neck 0.09; distance to first distinct 
segment 0.42; first segment, length 0.07, breadth 0.07; number of segments 
9; last segment, length 0.63, breadth 0.06. In two mounted specimens the 
length of the bothrium in each was 0.35, and the hooks, including the base, 
0.15. 
12. Pedibothrium brevispine gen. et sp. nov. 
(Plate 3, figs. 20-22; plate 4, figs. 23-25.) 
Bothria much as in P. longispine, except that, in the alcoholic specimens 
at least, they project farther in front of the hooks, and the free margins 
of the bothria are perhaps wider. The hooks are much smaller than those 
of P. longispine, and the prongs are unequal and unequally curved. The 
outer prong of each pair is curved much as in that species, but the inner 
prong is nearly straight and abruptly enlarged at the base. The common 
base of the two prongs of a hook is irregularly triangular. Neck distinct, 
with very conspicuous muscle bands, and is minutely spinose. 
There appears to be a considerable variety in the strobiles, some being 
short, with relatively few segments, others longer, with many immature seg- 
ments. In the longer strobiles the last segments are no farther advanced 
in the development of the reproductive organs than those on the shorter 
strobiles. 
The first segments broader than long, and, especially in the shorter type 
of strobile, have a tendency to become moniliform. Later they are much 
elongated, becoming six or more times as long as broad. The free segments 
are long-fusiform, eight or more times as long as broad, the posterior end 
being the more slender. The vagina and cirrus have their common aperture 
on the margin a little behind the middle. The vagina opens in front of the 
cirrus, proceeds almost at right angles to the long axis of the segment to 
the median line, then turns almost at right angles and passes near the median 
line to the ovaries. The ovaries are paired and lobed organs and lie nearly 
half-way between the reproductive cloaca and the posterior end. The vitel- 
