28 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 92 
eventually appear as a series of pouches. The vitelline glands are 
very numerous at the sides, and probably cover the dorsal and 
ventral faces of the segments, though in the segments prepared for 
study they were peeled off to make the deeper-lying organs visible. 
Host.—Galeocerdo arcticus (Faber). 
Location.—Spiral valve. 
Type specimen.—U.S.N.M. Helm. Coll. No. 36785. 
Remarks.—Although strikingly similar to Thysanocephalum thysano- 
cephalum (Linton, 1889), this species differs in general size and shape, 
proportions of segments, and particularly in the reticulations of the 
cuticle. ei 
DIPLOOTOBOTHRIUM, new genus 
Generic diagnosis.—Bothria two, provided with ciliated pits lat- 
erally. Proboscides shorter than their sheaths, armed with diagonal 
rows of strong, recurved hooks, changing to small, irregularly arranged 
hooklets on inner side. Contractile bulbs elongate, the retractor 
muscles attached near their upper ends; strobila long, connected 
with scolex by unsegmented neck. Reproductive organs completely 
doubled. 
Type.—Diploétobothrium springeri, new species. 
DIPLOOTOBOTHRIUM SPRINGERI, new species 
FIGuRE 2, e-2 
Specific description.—Scolex very broad and flat and very long 
(18 mm.). Bothria about 3 mm. long and 3.6 mm. broad. Width 
of head behind bothria 3.35 mm., nearly uniform for entire length. 
Proboscis sheaths in broad spirals, about five times as long as the 
bothria. Contractile bulbs about 3.5 mm. long and 0.47 mm. broad, 
the retractor muscles attached near the upper end. Proboscides 
about 2.5 mm. long and about 0.3 to 0.85 mm. broad exclusive of the 
books, 0.52 mm. broad including them. Hooks arranged in diagonal 
rows of 9 or 10 large, recurved, rose-thorn-shaped hooks, extending 
about two-thirds to three-fourths the distance around proboscis, 
the intervening area being occupied by small hooks more or less 
irregularly arranged; some of the small hooks near the base are only 
moderately curved and lack large bases. Largest hooks about 125y 
long, with a base of similar length; smallest hooks only about 20u 
long. Junction with strobila craspedote. Total length about 48 cm. 
Faint striations, indicating the beginning of segmentation, first 
visible about 4 mm. behind scolex. Mature segments, 20 to 30 cm. 
behind head, about 6 to 7 mm. broad and 3.75 to 4.75 mm. long. 
Terminal ripe segments about 5 to 6 mm. broad and 8 mm. long. 
Genital atria situated about middle of margin of segment in mature 
proglottids, posterior to middle in ripe ones. Paired ovaries and 
